High energy density vanadium electrolyte solutions, methods of preparation thereof and all-vanadium redox cells and batteries containing high energy vanadium electrolyte solutions

ABSTRACT

Disclosed is a method for preparing a high energy density (HED) electrolyte solution for use in an all-vanadium redox cell, a high energy density electrolyte solution, in particular an all-vanadium high energy density electrolyte solution, a redox cell, in particular an all-vanadium redox cell, comprising the high energy density electrolyte solution, a redox battery, in particular an all-vanadium redox battery, comprising the HED electrolyte solution, a process for recharging a discharged or partially discharged redox battery, in particular an all-vanadium redox battery, comprising the HED electrolyte solution, a process for the production of electricity from a charged redox battery, and in particular a charged all-vanadium redox battery, comprising the HED electrolyte, a redox battery/fuel cell and a process for the production of electricity from a redox battery/fuel cell. A method for stabilising an electrolyte solution for use in a redox cell, in particular for stabilising an electrolyte solution for use in an all-vanadium redox cell, a stabilised electrolyte solution, in particular an all-vanadium stabilised electrolyte solution, a redox cell, in particular an all-vanadium redox cell, comprising the stabilised electrolyte solution, a redox battery, in particular an all-vanadium redox battery, comprising the stabilised electrolyte solution, a process for recharging a discharged or partially discharged redox battery, in particular an all-vanadium redox battery, comprising the stabilised electrolyte solution, and a process for the production of electricity from a charged redox battery, and in particular a charged all-vanadium redox battery, comprising the stabilised electrolyte solution are disclosed. Also disclosed are a redox battery/fuel cell and a process for the production of electricity from a redox battery/fuel cell.

This is a divisional application of application Ser. No. 08/945,869, filed Feb. 24, 1998 now U.S. Pat. No. 6,468,688 which is a 371 of PCT/AU96/00268 filed May 3, 1996.

The present invention relates to a method for preparing a high energy density (HED) electrolyte solution for use in an all-vanadium redox cell; a high energy density electrolyte solution, in particular an all-vanadium high energy density electrolyte solution; a redox cell, in particular an all-vanadium redox cell comprising the high energy density electrolyte solution; a redox battery, in particular an all-vanadium redox battery comprising the HED electrolyte solution; a process for recharging a discharged or partially discharged redox battery, in particular an all-vanadium redox battery comprising the HED electrolyte solution; a process for the production of electricity from a charged redox battery, in particular a charged all-vanadium redox battery comprising the HED electrolyte; a redox battery/fuel cell; an immobilised cell; and a process for the production of electricity from a redox battery/fuel cell.

BACKGROUND OF THE INVENTION

Since the energy density available from batteries based on oxidation/reduction reactions of ions in the electrolyte solution is directly proportional to the concentration of redox ions undergoing oxidation or reduction in the electrolyte solution, the energy density available from batteries based on redox electrolyte solutions is limited generally by the maximum solubility of redox salts of the various oxidation states in the electrolyte solution, and in particular the redox component with the lowest solubility.

In the vanadium redox battery employing V(II)/V(III) and V(IV)/V(V) redox couples in the H₂SO₄ for the negative and positive ½-cell electrolyte solutions respectively, the vanadium concentration has been limited to less than 2M (about 1.8M) due to precipitation of V(II) and V(III) at low temperatures and the thermal precipitation of V(V) at high temperatures. The solubility of the V(II), V(III) and V(IV) ions increases with increasing temperatures, however, V(V) undergoes thermal precipitation to V₂O₅ at temperatures above 30° C.

For example if a 2M V(V) solution is exposed to temperatures of 30° C., a slight precipitate will start to form after 2 days, with heavy precipitation evident after only 4 days. At 40° C., a heavy precipitate will form after 2 days in a 2M V(V) solution. Even a 1.8M V(V) solution will precipitate after 6 days at 40° C.

This problem in use can be avoided by reducing the vanadium ion concentration to less than 1.8M for applications where the temperature is likely to exceed 40° C. and where the systems will be maintained in fully charged state for long periods. However in many applications it is not desirable to reduce the vanadium ion concentration below 2.0M since such a reduction effectively reduces the capacity and energy density of the battery.

In PCT/AU94/00711, a stabilised vanadium electrolyte solution was described which employed stabilising agents to inhibit the precipitation of vanadium from supersaturated solutions. Thus, 3M V(V) solution could be stabilised for several weeks by addition of 1–3 wt % glycerol, while 3M V(II) was stabilised by 1–3 wt % ammonium oxalate. A mixture of glycerol and ammonium oxalate inhibited precipitation of both V(II) and V(V) ions allowing a 3M vanadium electrolyte solution to operate successfully in a vanadium redox cell for close to six months. A large number of other organic and inorganic additives were also shown to inhibit the precipitation of vanadium from supersaturated solutions.

While these additives play a vital role in inhibiting precipitation of vanadium ions from supersaturated solutions of 2 to 4M vanadium, the author has found, surprisingly, that in the above case of V(V) solutions, at concentrations above 4M, the thermal precipitation reaction is completely inhibited even without the use of stabilising agents. Thus, a 5.5M V(V) solution produced by oxidation of 5.5M VOSO₄ in 2M H₂SO₄ showed no signs of precipitation even after 6 weeks at 50° C.

One of the objects of this invention is thus an all-vanadium redox battery employing vanadium solutions of greater than 2M and especially above 1.8M, more typically above 2M, even more typically above 3M, 4M or 5M concentration which can operate over a wide range of temperatures and operating conditions. To avoid the precipitation of V(II), V(III) or V(IV) ions at these concentrations the operating temperature of the system is maintained above 25° C. However, it has also been discovered that with the use of suitable stabilizing agents, the operating temperature can be extended below 25° C.

OBJECTS OF INVENTION

Accordingly, it is an object of the present invention to provide a method for preparing a high energy density (HED) electrolyte solution for use in an all-vanadium redox cell or all-vanadium redox battery.

Other objects include: providing (a) a HED all-vanadium electrolyte solution; (b) an all-vanadium redox cell comprising the HED electrolyte solution; (c) an all-vanadium redox battery comprising the HED electrolyte solution; (d) a process for recharging a discharged or partially discharged all-vanadium redox battery comprising the HED electrolyte solution; (e) a process for the production of electricity from a charged all-vanadium redox battery; (f) processes for producing a HED vanadium electrolyte solution, optionally highly supersaturated; (g) an all-vanadium redox charge cell; and (h) a process for charging a charge anolyte and a charge catholyte of an all-vanadium redox charge cell.

Another object of the present invention to provide a method for stabilising an electrolyte solution for use in a redox cell or redox battery, in particular for stabilising an electrolyte solution for use in an all-vanadium redox cell or all-vanadium redox battery.

It is a further object of the present invention to provide an improved all-vanadium redox cell and all-vanadium redox battery which can operate over a wide range of temperatures and operating conditions.

Another object is to provide a redox battery/fuel cell and a process for the production of electricity from a redox battery/fuel cell.

DISCLOSURE OF THE INVENTION

In this specification when reference is made to the electrolyte solutions of the all-vanadium redox charge cell the positive and negative electrolyte solutions are referred to as the catholyte and anolyte respectively. This is opposite to normal convention used in electrolytic processes but for convenience and consistency with nomenclature relating to batteries and other all-vanadium redox battery patent applications by the present applicant, the former convention has been adopted.

Throughout the specification the expression “acceptable” is used with reference to a precipitation rate of vanadium compounds from an electrolyte solution containing vanadium redox ions, which rate is such, that to be acceptable or suitable, the amount of any resultant precipitation is less than that which would substantially interfere with, and, typically less than that which would substantially reduce or limit, normal operation (including standing, charging and discharging operations) of an all-vanadium redox battery. In particular, “acceptable” includes reference to a precipitation rate of vanadium compounds from an electrolyte solution containing vanadium redox ions, which rate is such that the amount of any resultant precipitation does not substantially interfere with and substantially reduce catholyte and/or anolyte flow (eg flow of anolyte and catholyte solutions through the positive and negative compartments of an all-vanadium battery such as when it is pumped through such compartments) during normal operation of an all-vanadium redox flow battery (an all-vanadium flow battery being one in which the anolyte and catholyte are not immobilized).

Throughout the specification the expression “stabilising agent” refers to a substance that enables the upper concentration of redox ions in a redox electrolyte solution to be increased by adding an effective stabilising amount of the stabilising agent to the redox electrolyte solution. The stabilising agent may permit preparation of supersaturated solutions of redox ions in the redox electrolyte solution. The stabilising agent may also reduce or prevent precipitation of redox species from the redox electrolyte solution. The oxidation and reduction and other products of a compound/substance added to the redox electrolyte solution to stabilise the redox ions in solution are included within the definition of stabilising agent. The reason for this is that many of these compounds/substances may be converted to other products in the electrolyte solution. For example, organic compounds may be oxidised/reduced into other compounds or may combine with the vanadium ions/compounds to form new products or the products of the above compounds may combine with vanadium ions/compounds to form new products. These other products may act as stabilising agents. Thus throughout the specification and claims “stabilising agent” is to be taken to include products arising after addition of a compound/substance to the redox electrolyte solution to stabilise the redox ions in solution.

The energy density of redox flow batteries is determined by the concentration of the redox ions in the electrolyte solution. In the case of the vanadium redox flow battery, this has been limited to 2 moles/litre to avoid precipitation of V(II) or V(III) ions in the negative ½-cell electrolyte solution at temperatures below 15° C. and thermal precipitation of V(V) ions in the positive ½-cell solution at temperatures above 40° C.

It has now been found that one way of increasing the stability of the vanadium electrolyte solutions can be enhanced by adjusting the sulphuric acid concentration or total sulphate concentration. However, while an increased H2SO4 concentration will stabilise the V(V) ions at elevated temperatures, the increased sulphate level will reduce the saturation solubility of the V(II), V(III) and V(IV) ions. For the 2M vanadium electrolyte solutions, a total sulphate level of 5 moles per litre has been found to be the optimum concentration for providing adequate thermal stability for the V(V) ions while avoiding precipitation in the negative ½-cell electrolyte solution at the lower temperatures.

Because of the relatively slow rates of precipitation of the various ions at their corresponding temperature limits, it is often possible to extend the temperature range for short periods of time, especially if the battery is undergoing continuous charge-discharge cycling, as in the case of load-levelling applications. In applications such as remote area power supply or emergency back-up systems, where the battery can remain for several days or weeks at one state-of-charge (SOC), the vanadium ion concentration may need to be reduced below 2M if the electrolyte solution temperature is likely to fall below 15° C. or exceed 40° C. for significant periods.

Thus in very hot or cold climates where the battery is subjected to intermittent charge-discharge cycling, the vanadium ion concentration must be reduced to between 1.5 and 1.8M depending on the local climate and operating conditions. While this may extend the operating temperature range of the battery, it has the undesirable effect of reducing the energy density of the system. In applications such as electric vehicles, furthermore, vanadium ion concentrations significantly higher than 2M would be needed to make the vanadium battery viable. It is thus desirable to increase the vanadium ion concentration while avoiding precipitation of the redox ions during normal operation of the battery.

It is shown herein that the use of small amounts of stabilising agents such as a mixture of glycerine and ammonium sulphate, or D-fructose, enhances the stability of the vanadium ions by inhibiting their precipitation in supersaturated solutions. Thus, a stabilised 3M vanadium electrolyte solution subjected to continuous charge-discharge cycling in a cell for approximately 6 months was stable, while 2M V (II) and V(V) solutions were shown to have increased stability at 5° C. and 48° C. respectively in the presence of a wide range of organic and inorganic stabilising agents. Even a 5M supersaturated V(V) solution was found to be stable for several weeks at 48° C. in the presence of approximately 1% additives such as fructose and sorbitol.

Further work has shown however, that while these additives decrease the rate of precipitation in supersaturated solutions of V(II), V(III) and V(IV) ions at low temperatures, surprisingly, in the case of the V(V) ion, increasing the concentration above the previous 2M limit, actually increases its thermal stability even in the absence of any stabilising agents. While a 2M V(V) solution will precipitate after only 2 days at 50° C. a 5.4M V(V) solution shows no signs of precipitation even after 8 weeks at 48° C. What is even more surprising, however, is that the viscosity of the solution slowly decreases with time and its conductivity increases. The rate at which these changes occur increases with increasing temperature.

This surprising result thus makes it possible to enhance the thermal stability of a supersaturated positive ½-cell electrolyte solution by actually increasing the concentration of the vanadium ions. The upper temperature limit can thus be dramatically increased above the previous limit of 45° C. As the saturation solubility of the other vanadium ions is also higher at the higher temperatures, their precipitation is also avoided by operating the battery at elevated temperatures, thus avoiding the need to use stabilising agents. If a wider operating temperature range is required, however, stabilising agents can be employed to inhibit precipitation of V(II), V(III) and V(IV) ions at the lower temperatures.

In particular, in the case of vanadium electrolyte solution systems, it is now possible as a result of the present invention to achieve a substantial increase in the concentration of vanadium ions (especially V(V) ions, up to and including supersaturated concentrations, or greater than 1.8M to 15M or 2 to 15M or 3 to 10M or 4 to 10M and in particular 5.001 to 10M) in vanadium electrolyte solutions, especially vanadium redox electrolyte solutions.

Alternatively a V/O2 redox fuel cell using a HED V(II)/V(IV) electrolyte solution in the negative half cell and gaseous or liquid oxidant such as air, oxygen or hydrogen peroxide in the positive half cell can be employed.

Another approach to enabling the increase of the upper concentration of redox ions in a redox electrolyte solution (such as increasing the upper concentration of metal ions in an aqueous solution) is the addition of an effective stabilising amount of one or more stabilising agents to the solution. The inventors have also found surprisingly that the stabilising agent may also reduce precipitation of redox species from the redox electrolyte solution.

In particular, in the case of vanadium electrolyte solution systems, it has been found that it is possible to achieve a substantial increase in the concentration of vanadium ions (especially V(II), V(III), V(IV) and, in particular V(V) ions, up to and including supersaturated concentrations, or 0.1 to 15M or 1.801M or 2M or 2.01M to 10M and in particular 5.001 to 7.5M) in vanadium electrolyte solutions, especially vanadium redox electrolyte solutions, by the addition of relatively small amounts of one or more of stabilising agents to a vanadium electrolyte solution. Stabilising agents have been found which are capable of stabilising V(V), V(IV), V(III) and V(II) species and increasing their solubility.

Alternatively a V/O₂ redox fuel cell using a stabilised V(II)/V(IV) electrolyte solution in the negative half cell and gaseous or liquid oxidant such as air, oxygen or hydrogen peroxide in the positive half cell can be employed.

Typically the electrolyte solution is circulated separately through the positive and negative compartments.

SUMMARY OF THE INVENTION

According to a first embodiment of the present invention there is provided a method for preparing a high energy density (HED) electrolyte solution for use in an all-vanadium redox cell.

In particular there is provided a method of preparing a HED electrolyte solution for use in an all-vanadium redox cell, said solution containing an electrolyte, the method comprising:

-   a) adding a first substance to an electrolyte solution which first     substance when dissolved in the solution produces vanadium redox     ions in the solution; -   b) dissolving the first substance in the solution; -   b′) optionally dissolving a stabilising amount of stabilising agent     in the solution; -   c) optionally reducing the redox ions in the solution to a lower     oxidation state to generate a reductant capable of dissolving a     second substance in the solution which second substance when     dissolved in the solution produces vanadium redox ions in the     solution; -   c′) optionally oxidising the vanadium redox ions in the solution to     produce vanadium redox ions in the solution at a higher oxidation     state to generate an oxidant capable of dissolving a second     substance in the solution which second substance when dissolved in     the solution produces vanadium redox ions in the solution; -   d) optionally adding the second substance to the solution which     second substance when dissolved in the solution produces vanadium     redox ions in the solution; -   e) optionally dissolving the second substance in the solution; -   f) optionally reducing the redox ions in the solution to a lower     oxidation state to generate a reductant capable of dissolving more     of the second substance in the solution; -   f′) optionally oxidising the vanadium redox ions in the solution to     produce vanadium redox ions in the solution at a higher oxidation     state to generate an oxidant capable of dissolving more of the     second substance in the solution which second substance when     dissolved in the solution produces vanadium redox ions in the     solution; -   g) optionally repeating steps (d)–(f), or (d), (e) and (f′) or (d)     to (f′) to obtain the required concentration of the vanadium redox     ions in the solution.

The first substance may be the same as the second substance. The first substance may be different from the second substance.

For V(III) and/or V(IV) concentrations above 4M the solution temperature is generally higher than 25° C. to prevent the V(III) and/or V(IV) ions from crystallising or precipitating during electrolyte solution preparation, more typically 35° C. or above and even more typically 40° C. or above and yet even more typically 35–50° C.

Alternatively a HED V(V) electrolyte solution is prepared by dissolving and oxidising a V(II), V(III) or V(IV) salt dissolved or partially dissolved in a supporting electrolyte solution until fully dissolved and converted to V(V) oxidation state in the positive compartment of an electrolyte solution cell. The oxidation may optionally be conducted in the presence of a suitable stabilizing agent added to the solution.

In steps a) and e) said dissolving may be selected from the group consisting of chemically dissolving, simply dissolving, electrolytically dissolving and a combination of chemically dissolving and electrolytically dissolving.

According to a second embodiment of the present invention there is provided a HED electrolyte solution for use in a vanadium redox cell, the HED electrolyte solution comprising vanadium redox ions and an electrolyte. The HED electrolyte solution may be produced by the method of the first embodiment.

In particular there is provided an all-vanadium HED electrolyte solution for use in an all-vanadium redox cell, the electrolyte solution comprising vanadium redox ions in a high concentration and an electrolyte.

By vanadium redox ions in a high concentration is meant vanadium redox ions at above saturated concentration, typically above 1.8M up to and including supersaturated concentration.

The conditions of the electrolyte solution may be such as to reduce precipitation of the vanadium redox ions from the electrolyte solution to a rate whereby the all-vanadium electrolyte solution is acceptable for use in an all-vanadium redox battery.

Alternatively the conditions of the electrolyte solution may be controlled or maintained so as to reduce precipitation of the vanadium redox ions from the electrolyte solution to a rate whereby the all-vanadium electrolyte solution is acceptable for use in an all-vanadium redox battery.

In particular, the temperature and/or concentration of the electrolyte of solution may be such as to reduce precipitation of the vanadium redox ions from the electrolyte solution to a rate whereby the all-vanadium electrolyte solution is acceptable for use in an all-vanadium redox battery.

Generally the electrolyte solution contains vanadium redox ions which may or may not be present in the form of a redox couple(s). Typically the solution is an aqueous solution.

Included within the scope of the second embodiment is an electrolyte solution for use in a vanadium redox cell comprising an aqueous solution of vanadium ions and an acid.

The electrolyte solution may further comprise a stabilising amount of a stabilising agent, wherein the stabilising amount of the stabilising agent is less than that required to fully complex the vanadium redox ions in the electrolyte solution and is sufficient to reduce precipitation of the vanadium redox ions from the stabilised electrolyte solution to a rate whereby the stabilised all-vanadium electrolyte solution is acceptable for use in an all-vanadium redox battery. The stabilising agent may allow the operating temperature range of the electrolyte solution to be extended (e.g. 0–99° C., typically 0–95° C.).

The conditions of the solution may be maintained and/or controlled (e.g. the concentration of the electrolyte and/or the temperature of the solution and/or the stabilising amount of stabilising agent) to reduce precipitation of the vanadium redox ions from the electrolyte solution to a rate whereby the all-vanadium electrolyte solution is acceptable for use during at least one period in an all-vanadium redox battery, said period being selected from the group consisting of: between at least one recharging cycle of the battery; during at least one recharging cycle of the battery; between at least one recharging cycle of the battery and during at least one recharging cycle of the battery; between at least one discharging cycle of the battery; in a fully mixed state; in an over discharged state; during at least one discharging cycle of the battery; between at least one discharging cycle of the battery and during at least one discharging cycle of the battery; between at least one recharging cycle of the battery and during at least one recharging cycle of the battery and during at least one discharging cycle of the battery; between at least one recharging cycle of the battery and during at least one recharging cycle of the battery and during at least one discharging cycle of the battery; between at least one recharging cycle of the battery and during at least one recharging cycle of the battery and between at least one discharging cycle of the battery; between at least one recharging cycle of the battery and during at least one recharging cycle of the battery and between at least one discharging cycle of the battery and during at least one discharging cycle of the battery; during standing of the electrolyte solution in a fully charged state; during standing of the electrolyte solution in a partially charged state; during standing of the electrolyte solution in a fully discharged state; during standing of the electrolyte solution in a partially discharged state and during standing of the electrolyte solution in at least a partially uncharged state.

The vanadium ions may be in a concentration above 1.8M, more typically above 2M, even more typically above 2.5M or 3M, or more typically from 4M and more typically from 5.0001M up to and including a highly supersaturated concentration.

The vanadium redox ions may be in a concentration range up to and including a highly supersaturated concentration, such as above 1.8M, more typically above 2M, above 2.5M, 3M to 10M, 3M to 9M, 3M to 8M, 3M to 7M, 5M to 10M, 5.001M to 10M, 5.001M to 7.5M, 5.001M to 7.0M, and 5.001M to 6M, 3.0M to 12M, 4.0M to 12M, 5M to 12M, 5.001M to 12M, 5.001 to 8M. A HED electrolyte solution wherein the redox ions are selected from the group consisting of pentavalent vanadium ions, tetravalent vanadium ions, trivalent vanadium ions, divalent vanadium ions, a mixture of divalent and trivalent vanadium ions, a mixture of divalent and tetravalent vanadium ions, a mixture of trivalent and tetravalent vanadium ions, a mixture of divalent, trivalent and tetravalent vanadium ions, a mixture of divalent, trivalent, tetravalent and pentavalent vanadium ions, a mixture of tetravalent and pentavalent vanadium ions is particularly useful.

The HED electrolyte solution may contain a stabilizing amount of a suitable stabilizing agent if a wider operating temperature is required.

In particular there is provided a HED vanadium electrolyte solution for use in a vanadium redox cell comprising an aqueous solution of vanadium redox ions and an electrolyte solution, with the optional use of a stabilizing amount of a stabilizing agent for a wider operating temperature range.

According to a third embodiment of the present invention there is provided a vanadium redox cell or redox battery comprising a HED electrolyte solution according to the second embodiment. The HED electrolyte solution may optionally be produced by the method of the first embodiment.

The vanadium ions in the catholyte and/or anolyte may be above 1.8M, more typically above 2M, even more typically above 2.5M or 3M, or typically from 4M and more typically from 5M up to and including a highly supersaturated concentration.

According to a fourth embodiment of this invention there is provided an all-vanadium redox battery having a positive compartment containing a catholyte in electrical contact with a positive electrode, the catholyte comprising an electrolyte solution containing vanadium ions or vanadium redox ions, or a vanadium redox couple, comprising trivalent and/or tetravalent vanadium ions and/or pentavalent vanadium ions, a negative compartment containing an anolyte in electrical contact with a negative electrode, the anolyte comprising an electrolyte solution containing vanadium ions or vanadium redox ions, or a vanadium redox couple comprising tetravalent vanadium ions and/or trivalent vanadium ions and/or divalent vanadium ions, and a separator or membrane disposed between the positive and negative compartments and in contact with the catholyte and anolyte to provide ionic communication therebetween and wherein the catholyte and/or anolyte have a concentration above 1.8M, more typically above 2M, even more typically above 2.5M or 3M, or above 4M or typically from 5M up to or including a highly supersaturated concentration.

Optionally means are provided to maintain and/or control the operating conditions (e.g. temperature and/or electrolyte concentration) of the all-vanadium redox battery so as to substantially prevent or significantly reduce crystallisation or precipitation of vanadium substances/compounds from the catholyte and/or anolyte, typically above 20, more typically above 25° C. Alternatively, by using a stabilizing amount of a suitable stabilizing agent(s) a wider operating temperature can be achieved (e.g. above 0° C.).

The anolyte optionally has a concentration of tetravalent vanadium ions and/or trivalent and/or divalent vanadium ion above 1.8M, more typically above 2M, even more typically above 2.5M or 3M, or typically 5M up to and including a highly supersaturated concentration, 3M to 15M, 4M to 15M, 5.001 to 15M, 5.001 to 10M, optionally 5.001 to 9M, 4M to 9M or 3M to 9M.

The catholyte optionally has a concentration of pentavalent and/or tetravalent vanadium ions and/or trivalent vanadium ion concentration above 1.8M, more typically above 2M, even more typically above 2.5M or 3M, or typically 5M up to and including a supersaturated concentration, 3M to 15M, 4M to 15M, 5.001 to 15M, 5.001 to 10M, 3M to 10M, optionally 3M to 9M, 4M to 9M, 5.001 to 9M,

At least one of the catholyte and/or anolyte may comprise a HED electrolyte solution according to the second embodiment, or may be produced by the method of the first embodiment.

According to a fifth embodiment of the invention there is provided an all-vanadium redox battery system, comprising the all-vanadium redox battery of the fourth embodiment together with an anolyte reservoir for storing anolyte coupled to the negative compartment by anolyte supply and return lines via a pump, and a catholyte reservoir for storing catholyte coupled to the positive compartment by catholyte supply and return lines via a pump.

Optionally there is further provided an anolyte charge reservoir having anolyte charge supply and return line or lines for charging further anolyte which is to be delivered to the negative compartment and a catholyte charge reservoir having catholyte charge supply and return line or lines for charging further catholyte which is to be delivered to the positive compartment.

Optionally there is further provided pumping means associated with the anolyte and catholyte storage line or lines, and/or with the anolyte and catholyte charge line or lines, for pumping:

-   a) the catholyte through the catholyte storage line or lines, the     positive compartment and the catholyte charge line or lines; and -   b) the anolyte solution through the anolyte solution storage line or     lines, the negative compartment and the anolyte solution charge line     or lines.

Discharging and charging of the catholyte and anolyte may be conducted in sealed air tight cells and can be conducted under an inert atmosphere such as nitrogen, argon, helium or neon or mixtures thereof although an inert atmosphere can be avoided in a sealed system. During discharging and charging the electrolyte solutions may be stirred or agitated preferably by bubbling an inert gas and/or with a mechanical stirrer or by pumping the electrolyte solutions (i.e. the anolyte and catholyte) through the positive and negative compartments. To prevent air oxidation of the V(II) to V(III) in the anolyte, or to prevent oxygen effects in respect of the V(V) and V(III) and V(IV) in the catholyte, a blanket of an inert immiscible liquid can be used to cover the surface of the electrolyte in a layer about 0.5 cm to 5 cm in depth, typically about 1 cm deep, thus preventing the diffusion of air into the electrolyte.

Suitable immiscible liquids include paraffin oil or other hydrocarbon oil or a mineral oil, a vegetable oil eg arachis oil, olive oil, sesame oil, groundnut oil, peanut oil or coconut oil, a fish oil eg tuna oil, mackerel oil, sand eel oil, menhaden oil, anchovy oil, sardine oil, horse mackerel oil, salmon oil, herring oil, cod oil, capelin oil, pilchard oil, sprat oil, whale oil, Pacific oyster oil, Norway pout oil, seal oil and sperm whale oil or a plant oil eg pine oil, wheat germ oil and linseed oil or the like.

According to a sixth embodiment of this invention there is provided a process for recharging a discharged or partially discharged all-vanadium redox battery of the invention which process comprises providing electrical energy to the positive and negative electrodes to derive divalent vanadium ions in the anolyte and pentavalent vanadium ions in the catholyte.

During the process of recharging the conditions of the anolyte and/or catholyte solutions may be such so as to reduce precipitation of the vanadium redox ions from the electrolyte solution to a rate whereby the all-vanadium electrolyte solution is acceptable for use in an all-vanadium redox battery.

Alternatively, during the process of recharging the conditions of the anolyte and/or catholyte solutions may be maintained and/or controlled so as to reduce precipitation of the vanadium redox ions from the electrolyte solution to a rate whereby the all-vanadium electrolyte solution is acceptable for use in an all-vanadium redox battery.

In particular, temperature and/or electrolyte concentration of the anolyte and/or catholyte may be maintained and/or controlled during the process of recharging so as to reduce precipitation of the vanadium redox ions from the electrolyte solution to a rate whereby the all-vanadium electrolyte solution is acceptable for use in an all-vanadium redox battery.

Other conditions that may be maintained and/or controlled include sulphuric acid concentration and/or total sulphate concentration, pH's of the anolyte and/or catholyte, pumping rates of the anolyte and/or catholyte through the negative and positive compartments, concentrations of the various vanadium redox ions and/or couples in the anolyte and/or catholyte, and oxygen concentrations of the various vanadium redox ions and/or couples in the anolyte and/or catholyte. The pH and concentrations and pumping rates of the above mentioned species may be measured by appropriate probes or other appropriate means known in the art.

According to a seventh embodiment of this invention there is provided a process for the production of electricity from a charged redox battery of the invention which process comprises withdrawing electrical energy from the redox battery by loading an external circuit in electronic communication with the positive and negative electrode.

During the process of the production of electricity the conditions of the anolyte and/or catholyte solutions may be such so as to reduce precipitation of the vanadium redox ions from the electrolyte solution to a rate whereby the all-vanadium electrolyte solution is acceptable for use in an all-vanadium redox battery.

Alternatively, during the process of the production of electricity the conditions of the anolyte and/or catholyte solutions may be maintained and/or controlled so as to reduce precipitation of the vanadium redox ions from the electrolyte solution to a rate whereby the all-vanadium electrolyte solution is acceptable for use in an all-vanadium redox battery.

In particular, temperature and/or electrolyte concentration of the anolyte and/or catholyte may be maintained and/or controlled during the process of the production of electricity so as to reduce precipitation of the vanadium redox ions from the electrolyte solution to a rate whereby the all-vanadium electrolyte solution is acceptable for use in an all-vanadium redox battery.

Other conditions that may be maintained and/or controlled include sulphuric acid concentration and/or total sulphate concentration, pH's of the anolyte and/or catholyte, pumping rates of the anolyte and/or catholyte through the negative and positive compartments, concentrations of the various vanadium redox ions and/or couples in the anolyte and/or catholyte, and oxygen concentrations of the various vanadium redox ions and/or couples in the anolyte and/or catholyte. The pH and concentrations and pumping rates of the above mentioned species may be measured by appropriate probes or other appropriate means known in the art.

Typically the operating temperatures of the process for recharging a discharged or partially discharged all-vanadium redox battery of the invention and the process for the production of electricity from a charged redox battery of the invention are such so as to substantially prevent or significantly reduce crystallisation or precipitation of vanadium substances and/or compounds from the catholyte and/or anolyte, typically above 20, more typically above 25° C. typically up to about 90° C.

According to an eighth embodiment of this invention there is provided a redox battery/fuel cell having a positive compartment containing a catholyte in electrical contact with a positive electrode and a negative compartment containing an anolyte in electrical contact with a negative electrode; a separator or membrane disposed between the positive and negative compartments and in contact with the catholyte and anolyte to provide ionic communication therebetween, wherein the catholyte comprises redox ions selected from the group consisting of a catholyte redox couple, catholyte redox ions and a mixture of a catholyte redox couple and catholyte redox ions, and the anolyte comprises redox ions selected from the group consisting of an anolyte redox couple, anolyte redox ions and a mixture of an anolyte redox couple and anolyte redox ions.

Typically at least one of the anolyte and/or catholyte has a vanadium ion concentration above 1.8M, more typically above 2M, even more typically above 2.5M or 3M, or typically above 5M.

Typically the positive electrode is selected from the group consisting of an oxidising gas electrode, an oxidising liquid electrode, an oxygen electrode and an air electrode.

Optionally the positive electrode has a gas contacting portion disposed so as to be capable of contacting a gas selected from the group consisting of an oxidising gas, oxygen, an oxygen containing gas, and air. Alternatively the positive electrode contacts a catholyte containing an oxidising solution such as hydrogen peroxide.

Typically the negative electrode is either a reducing gas electrode or a hydrogen gas electrode.

Optionally the negative electrode has a gas contacting portion disposed so as to be capable of contacting a gas selected from the group consisting of a reducing gas, a hydrogen containing gas, and hydrogen.

Optionally means are provided to maintain and/or control the operating conditions (e.g. temperature and/or electrolyte concentration) of the all-vanadium redox battery/fuel cell so as to substantially prevent or significantly reduce crystallisation or precipitation of vanadium substances/compounds from the catholyte and/or anolyte, typically above 20, more typically above 25° C. Optionally, by adding a stabilizing amount of a suitable stabilizing agent(s) to the anolyte and/or catholyte a wider operating temperature can be achieved (e.g. above 0° C.).

According to a ninth embodiment of this invention there is provided a process for the production of electricity from a redox battery/fuel cell of the invention when said battery/fuel cell is charged or partially charged, which process comprises withdrawing electrical energy from the redox battery/fuel cell by loading an external circuit in electronic communication with the positive and negative electrode.

The redox ions may be above 1.8M, more typically above 2M, even more typically above 2.5M or 3M, or typically from 5M up to and including a highly supersaturated concentration.

Further Embodiments of this Invention Are:

A. A HED all-vanadium electrolyte solution for use in an all-vanadium redox battery, the HED electrolyte solution comprising vanadium redox ions and an electrolyte at an operating temperature above 25° C. to reduce precipitation of the V(II), V(III) or V(IV) ions.

B. An all-vanadium redox battery having a positive compartment containing a catholyte in electrical contact with a positive electrode, the catholyte comprising an electrolyte solution containing vanadium ions selected from the group consisting of trivalent vanadium ions, tetravalent vanadium ions, pentavalent vanadium ions, and a mixture of at least two of trivalent vanadium ions, tetravalent vanadium ions, and pentavalent vanadium ions, a negative compartment containing an anolyte in electrical contact with a negative electrode, the anolyte comprising an electrolyte solution containing vanadium ions selected from the group consisting of tetravalent vanadium ions, trivalent vanadium ions, divalent vanadium ions, and a mixture of at least two of divalent vanadium ions, trivalent vanadium ions, and tetravalent vanadium ions, and a separator or membrane disposed between the positive and negative compartments and in contact with the catholyte and anolyte to provide ionic communication therebetween and wherein at least one of the anolyte and catholyte is a HED all-vanadium electrolyte solution for use in an all-vanadium redox battery, the HED electrolyte solution comprising greater than 3M or typically above 5M vanadium redox ions and an electrolyte and optionally means to maintain and/or control the operating temperature of the all-vanadium redox battery so as to substantially reduce crystallisation or precipitation of vanadium substances/compounds from the catholyte and/or anolyte, typically above 20, more typically above 25° C., to a rate whereby the HED all-vanadium electrolyte solution is acceptable for use in an all-vanadium redox battery. The electrolytes may optionally contain a stabilising amount of a stabilising agent.

C. A process for recharging an all-vanadium redox battery according to B, when said battery is discharged or partially discharged, which process comprises providing electrical energy to the positive and negative electrodes to derive divalent vanadium ions in the anolyte and pentavalent vanadium ions in the catholyte.

D. A process for the production of electricity from an all-vanadium redox battery according to B, when said battery is charged or partially charged, which process comprises withdrawing electrical energy from the redox battery by loading an external circuit in electronic communication with the positive and negative electrode.

E. A method of preparing a HED all-vanadium electrolyte solution for use in an all-vanadium redox battery, the HED electrolyte solution comprising higher than 3M vanadium redox ions and an electrolyte, the method comprising:

(a) adding a first substance to the solution which first substance when dissolved in the solution produces vanadium redox ions in the solution;

(b) dissolving the first substance in the solution;

(c) optionally reducing the vanadium redox ions in the solution to a lower oxidation state to generate a reductant capable of dissolving a second substance in the solution which second substance when dissolved in the solution produces vanadium redox ions in the solution;

(d) optionally adding the second substance to the solution which second substance when dissolved in the solution produces vanadium redox ions in the solution;

(e) optionally dissolving the second substance in the solution;

(f) optionally reducing the vanadium redox ions in the solution to a lower oxidation state to generate a reductant capable of dissolving more of the second substance in the solution;

(g) optionally repeating steps (a)–(f) or (d)–(f) to obtain the required concentration of the vanadium redox ions in the solution.

F. A method of preparing a HED all-vanadium electrolyte solution for use in an all-vanadium redox battery, the HED electrolyte solution comprising higher than 3M vanadium redox ions and an electrolyte, the method comprising:

(a) adding a first substance to the solution which first substance when dissolved in the solution produces vanadium redox ions in the solution;

(b) dissolving the first substance in the solution;

(b′) optionally oxidising the vanadium redox ions in the solution to produce vanadium redox ions in the solution at a higher oxidation state;

(c) optionally reducing the vanadium redox ions at a higher oxidation state in the solution to a lower oxidation state to generate a reductant capable of dissolving a second substance in the solution which second substance when dissolved in the solution produces vanadium redox ions in the solution;

(d) optionally adding the second substance to the solution which second substance when dissolved in the solution produces vanadium redox ions in the solution;

(e) optionally dissolving the second substance in the solution;

(e′) optionally oxidising the vanadium redox ions in the solution to produce vanadium redox ions in the solution at a higher oxidation state;

(f) optionally reducing the vanadium redox ions at a higher oxidation state in the solution to a lower oxidation state to generate a reductant capable of dissolving more of the second substance in the solution;

(g) optionally repeating steps (a)–(f) or (d)–(f) to obtain the required concentration of the vanadium redox ions in the solution.

G A HED vanadium electrolyte solution produced by the method of either of embodiments E or F.

H. An all-vanadium redox battery of the invention the temperature of at least one of the anolyte or catholyte being such as to reduce precipitation of the vanadium redox ions from at least one of the anolyte or catholyte to a rate whereby the all-vanadium electrolyte solution is acceptable for use in an all-vanadium redox battery.

I. An all-vanadium redox battery of the invention, the concentration of at least one of the anolyte or catholyte being such as to reduce precipitation of the vanadium redox ions from at least one of the anolyte or catholyte to a rate whereby the all-vanadium electrolyte solution is acceptable for use in an all-vanadium redox battery.

J. An all-vanadium redox battery of the invention, the concentration of at least one of the anolyte or catholyte and the temperature of the solution being such as to reduce precipitation of the vanadium redox ions from at least one of the anolyte or catholyte to a rate whereby the all-vanadium electrolyte solution is acceptable for use in an all-vanadium redox battery.

Generally the operating temperatures of the methods and processes of the invention are so as to substantially reduce or prevent crystallisation or precipitation of vanadium substances/compounds, typically above 20, more typically above 25° C. or above 0° C. in the presence of a stabilizing amount of stabilizing agent(s).

K. An immobilized HED all-vanadium electrolyte solution for use in an immobilized electrolyte solution containing all-vanadium redox battery, comprising the HED electrolyte solution of the invention, including embodiment A, immobilized with an effective immobilising amount of an immobilising agent.

L. An immobilized stabilised all-vanadium electrolyte solution for use in an immobilized electrolyte solution containing all-vanadium redox battery, comprising the HED electrolyte solution of the invention, including embodiment A, immobilized with an effective immobilising amount of an immobilising agent selected from the group consisting of gels, gums, Xanthan gum, Guar gum, starch, furcellaran, hypnean, dextran, tamarind, alginates, pectic gels, sodium pectate, alkylcellulose hydrophilic colloids, hydroxyalkylcellulose, carboxyalkylcellulose, hydroxypropylmethyl cellulose, sodium carboxymethylcellulose, potassium carboxymethyl cellulose, hydroxymethylcellulose, ethyl succinylated Cellulose, succinylated zein, carboxymethylcellulose, sodium poly (styrene sulphonate) with poly (vinyl methyl pyridinium) chloride, sodium poly (styrene sulphonate) with poly (vinyl benzyl trimethyl ammonium) chloride, vinyl acetate homopolymer, polyvinyl alcohol resin, carboxypolymethylene, sodium alginate, a mixture of gelatin and sodium alginate, potassium alginate, gelatine, acacia gum, deacetylated gellan gum, karaya gum, locust bean gum, tragacanth gum, agar-agar, algin and derivatives and alkali metal salts thereof, thereof, carrageenin, furcellaran, carrageenan, carob bean gum, oat gum, pectin, methyl cellulose, (hydroxypropyl)methyl cellulose, sodium carboxymethyl cellulose, polygalacturonic acid and mixtures thereof.

M. An immobilized electrolyte solution containing all-vanadium redox battery having a positive compartment containing an immobilized catholyte in electrical contact with a positive electrode, the immobilized catholyte comprising an effective immobilizing amount of a catholyte immobilizing agent and an electrolyte containing vanadium ions selected from the group consisting of trivalent vanadium ions, tetravalent vanadium ions, pentavalent vanadium ions, and a mixture of at least two of trivalent vanadium ions, tetravalent vanadium ions, and pentavalent vanadium ions, a negative compartment containing an immobilized anolyte in electrical contact with a negative electrode, the anolyte comprising an effective immobilizing amount of an anolyte immobilizing agent and an electrolyte containing vanadium ions selected from the group consisting of tetravalent vanadium ions, trivalent vanadium ions, divalent vanadium ions, and a mixture of at least two of divalent vanadium ions, trivalent vanadium ions, and tetravalent vanadium ions, and a separator or membrane disposed between the positive and negative compartments and in contact with the catholyte and anolyte to provide ionic communication therebetween and optionally means to maintain the operating temperature of the battery so as to substantially prevent or significantly reduce crystallisation or precipitation of vanadium substances/compounds from the catholyte and/or anolyte, typically above 20, more typically above 25° C.

N. A process for recharging an immobilized electrolyte solution containing all-vanadium redox battery according to embodiment M, when said battery is discharged or partially discharged, which process comprises providing electrical energy to the positive and negative electrodes to derive divalent vanadium ions in the anolyte and pentavalent vanadium ions in the catholyte.

O. A process for the production of electricity from an immobilized electrolyte solution containing all-vanadium redox battery according to embodiment M, when said battery is charged or partially charged, which process comprises withdrawing electrical energy from the redox battery by loading an external circuit in electronic communication with the positive and negative electrode.

P. A method of preparing an immobilized all-vanadium electrolyte solution for use in an immobilized electrolyte solution containing all-vanadium redox battery, comprising preparing the all-vanadium electrolyte solution according to the method of the invention including by the method of any one of embodiments E to F and immobilizing the all-vanadium electrolyte solution with an effective immobilizing amount of an immobilizing agent.

Q. A method of preparing an immobilized all-vanadium electrolyte solution for use in an immobilized electrolyte solution containing all-vanadium redox battery, comprising preparing the all-vanadium electrolyte solution according to the method of the invention, including the method of any one of embodiments E to F and immobilizing the all-vanadium electrolyte solution with an effective immobilizing amount of an immobilizing agent wherein the immobilizing agent is selected from the group consisting of gels, gums, Xanthan gum, sodium hexametaphosphate, myo-inositol, Guar gum, starch, furcellaran, hypnean, dextran, tamarind, alginates, pectic gels, sodium pectate, potassium pectate, alkylcellulose hydrophilic colloids, hydroxyalkylcellulose, carboxyalkylcellulose, hydroxypropylmethyl cellulose, sodium carboxymethylcellulose, potassium carboxymethyl cellulose, hydroxymethylcellulose, ethyl succinylated Cellulose, succinylated zein, carboxymethylcellulose, sodium poly (styrene sulphonate) with poly (vinyl methyl pyridinium) chloride, sodium poly (styrene sulphonate) with poly (vinyl benzyl trimethyl ammonium) chloride, vinyl acetate homopolymer, polyvinyl alcohol resin, carboxypolymethylene, sodium alginate, gelatin, a mixture of gelatin and sodium alginate, a mixture of gelatin and potassium alginate, potassium alginate, gelatine, acacia gum, deacetylated gellan gum, karaya gum, locust bean gum, tragacanth gum, agar-agar, algin and derivatives and alkali metal salts thereof, thereof, carrageenin, furcellaran, carrageenan, carob bean gum, oat gum, pectin, methyl cellulose, (hydroxypropyl)methyl cellulose, polygalacturonic acid and mixtures thereof.

Generally the temperature of the immobilized all-vanadium electrolyte solution of the invention is at such a level so as to substantially reduce or prevent crystallisation or precipitation of vanadium substances/compounds, typically above 20, more typically above 25° C.

Typically in the HED electrolyte solution the vanadium ions are present in the solution above 1.8M, more typically above 2M, even more typically above 2.5M or 3M, or typically from 5M up to and including a highly supersaturated concentration.

The HED electrolyte solution is typically an aqueous solution, and the electrolyte is selected from the group consisting of H₂SO₄, trifluoromethanesulphonic acid, Na₂SO₄, ammonium sulphate, K₂SO₄, H₃PO₄, Na₃PO₄, K₃PO₄, KNO3, NaNO₃, sulphonic acid, C₆–C₁₄ arylsulphonic acid such as p-toluenesulphonic acid, benzenesulphonic acid, naphthalenesulphonic acid, C₁–C₆ alkylsulphonic acid such as methylsulphonic acid and ethylsulphonic acid, acetic acid and mixtures thereof, more typically the electrolyte is H₂SO₄.

Typically the HED solution is an aqueous solution and the vanadium redox ions (and electrolyte e.g. H₂SO₄ alternatively expressed as total sulphate concentration) are (each) present in a range selected from the group consisting of 1.801M, optionally 2M up to and including a highly supersaturated concentration, aM, bM, a concentration in the range aM–bM, and a concentration range in the range aM–bM, where a is selected from the group consisting of a value presented in the column headed “a” in Table A below at one of entries 1–24, and b is selected from the group of the values presented in the column headed “b” adjacent the corresponding “a” entry:

TABLE A Entry a b 1 2 2.01, 2.25, 2.5, 2.75, 3, 3.01, 3.25, 3.5, 3.75, 4, 4.25, 4.5, 4.75, 5, 5.01, 5.25, 5.5, 5.75, 6, 6.25, 6.5, 6.75, 7, 7.25, 7.5, 7.75, 8, 8.25, 8.5, 8.75, 9, 9.25, 9.5, 9.75, 10, 10.25, 10.5, 10.75, 11, 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5 2 2.01 2.25, 2.5, 2.75, 3, 3.01, 3.25, 3.5, 3.75, 4, 4.25, 4.5, 4.75, 5, 5.01, 5.25, 5.5, 5.75, 6, 6.25, 6.5, 6.75, 7, 7.25, 7.5, 7.75, 8, 8.25, 8.5, 8.75, 9, 9.25, 9.5, 9.75, 10, 10.25, 10.5, 10.75, 11, 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5 3 2.25 2.5, 2.75, 3, 3.01, 3.25, 3.5, 3.75, 4, 4.25, 4.5, 4.75, 5, 5.01, 5.25, 5.5, 5.75, 6, 6.25, 6.5, 6.75, 7, 7.25, 7.5, 7.75, 8, 8.25, 8.5, 8.75, 9, 9.25, 9.5, 9.75, 10, 10.25, 10.5, 10.75, 11, 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5 4 2.5 2.75, 3, 3.01, 3.25, 3.5, 3.75, 4, 4.25, 4.5, 4.75, 5, 5.01, 5.25, 5.5, 5.75, 6, 6.25, 6.5, 6.75, 7, 7.25, 7.5, 7.75, 8, 8.25, 8.5, 8.75, 9, 9.25, 9.5, 9.75, 10, 10.25, 10.5, 10.75, 11, 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5 5 2.75 3, 3.01, 3.25, 3.5, 3.75, 4, 4.25, 4.5, 4.75, 5, 5.01, 5.25, 5.5, 5.75, 6, 6.25, 6.5, 6.75, 7, 7.25, 7.5, 7.75, 8, 8.25, 8.5, 8.75, 9, 9.25, 9.5, 9.75, 10, 10.25, 10.5, 10.75, 11, 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5 6 3 3.01, 3.25, 3.5, 3.75, 4, 4.25, 4.5, 4.75, 5, 5.01, 5.25, 5.5, 5.75, 6, 6.25, 6.5, 6.75, 7, 7.25, 7.5, 7.75, 8, 8.25, 8.5, 8.75, 9, 9.25, 9.5, 9.75, 10, 10.25, 10.5, 10.75, 11, 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5 7 3.01 3.25, 3.5, 3.75, 4, 4.25, 4.5, 4.75, 5, 5.01, 5.25, 5.5, 5.75, 6, 6.25, 6.5, 6.75, 7, 7.25, 7.5, 7.75, 8, 8.25, 8.5, 8.75, 9, 9.25, 9.5, 9.75, 10, 10.25, 10.5, 10.75, 11, 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5 8 3.25 3.5, 3.75, 4, 4.25, 4.5, 4.75, 5, 5.01, 5.25, 5.5, 5.75, 6, 6.25, 6.5, 6.75, 7, 7.25, 7.5, 7.75, 8, 8.25, 8.5, 8.75, 9, 9.25, 9.5, 9.75, 10, 10.25, 10.5, 10.75, 11, 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5 9 3.5 3.75, 4, 4.25, 4.5, 4.75, 5, 5.01, 5.25, 5.5, 5.75, 6, 6.25, 6.5, 6.75, 7, 7.25, 7.5, 7.75, 8, 8.25, 8.5, 8.75, 9, 9.25, 9.5, 9.75, 10, 10.25, 10.5, 10.75, 11, 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5 10 3.75 4, 4.25, 4.5, 4.75, 5, 5.01, 5.25, 5.5, 5.75, 6, 6.25, 6.5, 6.75, 7, 7.25, 7.5, 7.75, 8, 8.25, 8.5, 8.75, 9, 9.25, 9.5, 9.75, 10, 10.25, 10.5, 10.75, 11, 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5 11 4 4.25, 4.5, 4.75, 5, 5.01, 5.25, 5.5, 5.75, 6, 6.25, 6.5, 6.75, 7, 7.25, 7.5, 7.75, 8, 8.25, 8.5, 8.75, 9, 9.25, 9.5, 9.75, 10, 10.25, 10.5, 10.75, 11, 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5 12 4.25 4.5, 4.75, 5, 5.01, 5.25, 5.5, 5.75, 6, 6.25, 6.5, 6.75, 7, 7.25, 7.5, 7.75, 8, 8.25, 8.5, 8.75, 9, 9.25, 9.5, 9.75, 10, 10.25, 10.5, 10.75, 11, 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5 13 4.5 4.75, 5, 5.01, 5.25, 5.5, 5.75, 6, 6.25, 6.5, 6.75, 7, 7.25, 7.5, 7.75, 8, 8.25, 8.5, 8.75, 9, 9.25, 9.5, 9.75, 10, 10.25, 10.5, 10.75, 11, 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5 14 4.75 5, 5.01, 5.25, 5.5, 5.75, 6, 6.25, 6.5, 6.75, 7, 7.25, 7.5, 7.75, 8, 8.25, 8.5, 8.75, 9, 9.25, 9.5, 9.75, 10, 10.25, 10.5, 10.75, 11, 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5 15 5 5.01, 5.25, 5.5, 5.75, 6, 6.25, 6.5, 6.75, 7, 7.25, 7.5, 7.75, 8, 8.25, 8.5, 8.75, 9, 9.25, 9.5, 9.75, 10, 10.25, 10.5, 10.75, 11, 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5 16 5.01 5.25, 5.5, 5.75, 6, 6.25, 6.5, 6.75, 7, 7.25, 7.5, 7.75, 8, 8.25, 8.5, 8.75, 9, 9.25, 9.5, 9.75, 10, 10.25, 10.5, 10.75, 11, 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5 17 5.25 5.5, 5.75, 6, 6.25, 6.5, 6.75, 7, 7.25, 7.5, 7.75, 8, 8.25, 8.5, 8.75, 9, 9.25, 9.5, 9.75, 10, 10.25, 10.5, 10.75, 11, 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5 18 5.5 5.75, 6, 6.25, 6.5, 6.75, 7, 7.25, 7.5, 7.75, 8, 8.25, 8.5, 8.75, 9, 9.25, 9.5, 9.75, 10, 10.25, 10.5, 10.75, 11, 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5 19 5.75 6, 6.25, 6.5, 6.75, 7, 7.25, 7.5, 7.75, 8, 8.25, 8.5, 8.75, 9, 9.25, 9.5, 9.75, 10, 10.25, 10.5, 10.75, 11, 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5 20 6 6.25, 6.5, 6.75, 7, 7.25, 7.5, 7.75, 8, 8.25, 8.5, 8.75, 9, 9.25, 9.5, 9.75, 10, 10.25, 10.5, 10.75, 11, 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5 21 7 7.25, 7.5, 7.75, 8, 8.25, 8.5, 8.75, 9, 9.25, 9.5, 9.75, 10, 10.25, 10.5, 10.75, 11, 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5 22 8 8.25, 8.5, 8.75, 9, 9.25, 9.5, 9.75, 10, 10.25, 10.5, 10.75, 11, 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5 23 9 9.25, 9.5, 9.75, 10, 10.25, 10.5, 10.75, 11, 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5 24 10 10.25, 10.5, 10.75, 11, 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5

Advantageously where a sulphate electrolyte is used (e.g. sulphuric acid) the mole:mole ratio of vanadium ions:total sulphate is from 0.1 to 1, typically 2:5. Thus for a 2M vanadium ion solution 5M total sulphate is typically used. For 1.801–5M vanadium ion concentration 5–7M total sulphate is typically used as the electrolyte concentration.

Advantageously the HED electrolyte solution is selected from the group consisting of a HED electrolyte anolyte solution and a HED electrolyte catholyte solution.

Generally the redox ions are selected from the group consisting of pentavalent vanadium ions, tetravalent vanadium ions, trivalent vanadium ions, divalent vanadium ions, a mixture of divalent and trivalent vanadium ions, a mixture of divalent and tetravalent vanadium ions, a mixture of trivalent and tetravalent vanadium ions, a mixture of divalent, trivalent and tetravalent vanadium ions, a mixture of divalent, trivalent, tetravalent and pentavalent vanadium ions, a mixture of trivalent, tetravalent and pentavalent vanadium ions and a mixture of tetravalent and pentavalent vanadium ions.

Advantageously the HED electrolyte solution without stabilising agents is maintained, controlled and/or operated in a redox cell, redox battery or redox battery/fuel cell at a temperature selected from the group consisting of e° C., f° C., a temperature in the range e° C.–f° C. and a temperature range in the range e° C.–f° C. where e is selected from the group consisting of a value presented in the column headed “e” in Table B below at one of entries 1–9, and f is selected from the group of the values presented in the column headed “f” adjacent the corresponding “e” entry:

TABLE B Entry e f 1 20 25, 27, 30, 33, 35, 37, 40, 43, 45, 48, 50, 55, 60, 65, 70, 75, 80, 90 2 25 27, 30, 33, 35, 37, 40, 43, 45, 48, 50, 55, 60, 65, 70, 75, 80, 90 3 30 33, 35, 37, 40, 43, 45, 48, 50, 55, 60, 65, 70, 75, 80, 90 4 35 37, 40, 45, 50, 55, 60, 65, 70, 75, 80, 90 5 40 45, 50, 55, 60, 65, 70, 75, 80, 90 6 45 50, 55, 60, 65, 70, 75, 80, 90 7 50 55, 60, 65, 70, 75, 80, 90 8 55 60, 65, 70, 75, 80, 90 9 60 65, 70, 75, 80, 90 10 65 70, 75, 80, 90

In the all-vanadium battery of the invention the catholyte may be a HED all-vanadium electrolyte solution. The vanadium ions in the catholyte may be above 1.8M, more typically above 2M, even more typically above 2.5M or 3M, or typically 5M and above (e.g. up to 20M).

In the all-vanadium battery of the invention the anolyte may be a HED all-vanadium electrolyte solution. The vanadium ions in the anolyte may be above 1.8M, more typically above 2M, even more typically above 2.5M or 3M, or typically 5M up to 10M or 20M.

In the all-vanadium battery of the invention the anolyte and catholyte may be HED all-vanadium electrolyte solutions. The vanadium ions in the anolyte and the catholyte may be above 1.8M, more typically above 2M, even more typically above 2.5M or 3M, or typically from 5M up to 10M or 20M.

In the methods of the invention the concentration of vanadium redox ions in the solution may be further increased by removing water (eg by evaporation, vacuum evaporation, pervaporation) from the solution containing the required concentration of vanadium ions in the solution.

In the methods of the invention a concentrate comprising vanadium redox ions in the solution may be formed by removing water from the solution containing the required concentration of vanadium ions in the solution and further comprising adding water to the concentrate in an amount whereby the vanadium redox ions are at a predetermined concentration in the solution.

In the methods of the invention that use two substances the first substance may be different from the second substance. Typically the first substance is the same as the second substance and is selected from vanadium pentoxide, ammonium metavanadate, V₂O₃, V₂O₄, and VOSO₄, NH₄VO₃.

In the immobilised electrolyte containing all-vanadium battery typically the immobilising agent is present in a range selected from the group consisting of w % to x % wt/vol of the solution, w % to x % wt/wt of the solution, w % to x % wt/wt of the vanadium ions in the solution, w % to x % vol/vol of the solution, w % to x % vol/wt of the solution, w % to x % vol/wt of the vanadium ions in the solution, and w % to x % mole/mole of the vanadium ions in the solution, where w is selected from the group consisting of a value presented in the column headed “w” in Table C below at one of entries 1–25, and x is selected from the group of the values presented in the column headed “x” adjacent the corresponding “w” entry.

TABLE C Entry w x 1 1 1.25, 1.5, 1.75, 2, 2.25, 2.5, 2.75, 3, 3.25, 3.5, 3.75, 4, 4.25, 4.5, 4.75, 5, 5.25, 5.5, 5.75, 6, 6.25, 6.5, 6.75, 7, 7.25, 7.5, 7.75, 8, 8.25, 8.5, 8.75, 9, 9.25, 9.5, 9.75, 10, 10.25, 10.5, 10.75, 11, 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5, 19, 19.5, 20, 25, 30, 35, 40, 45, 50, 55, 60, 70, 80 2 1.25 1.5, 1.75, 2, 2.25, 2.5, 2.75, 3, 3.25, 3.5, 3.75, 4, 4.25, 4.5, 4.75, 5, 5.25, 5.5, 5.75, 6, 6.25, 6.5, 6.75, 7, 7.25, 7.5, 7.75, 8, 8.25, 8.5, 8.75, 9, 9.25, 9.5, 9.75, 10, 10.25, 10.5, 10.75, 11, 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5, 19, 19.5, 20, 25, 30, 35, 40, 45, 50, 55, 60, 70, 80 3 1.5 1.75, 2, 2.25, 2.5, 2.75, 3, 3.25, 3.5, 3.75, 4, 4.25, 4.5, 4.75, 5, 5.25, 5.5, 5.75, 6, 6.25, 6.5, 6.75, 7, 7.25, 7.5, 7.75, 8, 8.25, 8.5, 8.75, 9, 9.25, 9.5, 9.75, 10, 10.25, 10.5, 10.75, 11, 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5, 19, 19.5, 20, 25, 30, 35, 40, 45, 50, 55, 60, 70, 80 4 1.75 2, 2.25, 2.5, 2.75, 3, 3.25, 3.5, 3.75, 4, 4.25, 4.5, 4.75, 5, 5.25, 5.5, 5.75, 6, 6.25, 6.5, 6.75, 7, 7.25, 7.5, 7.75, 8, 8.25, 8.5, 8.75, 9, 9.25, 9.5, 9.75, 10, 10.25, 10.5, 10.75, 11, 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5, 19, 19.5, 20, 25, 30, 35, 40, 45, 50, 55, 60, 70, 80 5 2 2.25, 2.5, 2.75, 3, 3.25, 3.5, 3.75, 4, 4.25, 4.5, 4.75, 5, 5.25, 5.5, 5.75, 6, 6.25, 6.5, 6.75, 7, 7.25, 7.5, 7.75, 8, 8.25, 8.5, 8.75, 9, 9.25, 9.5, 9.75, 10, 10.25, 10.5, 10.75, 11, 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5, 19, 19.5, 20, 25, 30, 35, 40, 45, 50, 55, 60, 70, 80 6 2.25 2.5, 2.75, 3, 3.25, 3.5, 3.75, 4, 4.25, 4.5, 4.75, 5, 5.25, 5.5, 5.75, 6, 6.25, 6.5, 6.75, 7, 7.25, 7.5, 7.75, 8, 8.25, 8.5, 8.75, 9, 9.25, 9.5, 9.75, 10, 10.25, 10.5, 10.75, 11, 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5, 19, 19.5, 20, 25, 30, 35, 40, 45, 50, 55, 60, 70, 80 7 2.5 2.75, 3, 3.25, 3.5, 3.75, 4, 4.25, 4.5, 4.75, 5, 5.25, 5.5, 5.75, 6, 6.25, 6.5, 6.75, 7, 7.25, 7.5, 7.75, 8, 8.25, 8.5, 8.75, 9, 9.25, 9.5, 9.75, 10, 10.25, 10.5, 10.75, 11, 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5, 19, 19.5, 20, 25, 30, 35, 40, 45, 50, 55, 60, 70, 80 8 2.75 3, 3.25, 3.5, 3.75, 4, 4.25, 4.5, 4.75, 5, 5.25, 5.5, 5.75, 6, 6.25, 6.5, 6.75, 7, 7.25, 7.5, 7.75, 8, 8.25, 8.5, 8.75, 9, 9.25, 9.5, 9.75, 10, 10.25, 10.5, 10.75, 11, 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5, 19, 19.5, 20, 25, 30, 35, 40, 45, 50, 55, 60, 70, 80 9 3 3.25, 3.5, 3.75, 4, 4.25, 4.5, 4.75, 5, 5.25, 5.5, 5.75, 6, 6.25, 6.5, 6.75, 7, 7.25, 7.5, 7.75, 8, 8.25, 8.5, 8.75, 9, 9.25, 9.5, 9.75, 10, 10.25, 10.5, 10.75, 11, 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5, 19, 19.5, 20, 25, 30, 35, 40, 45, 50, 55, 60, 70, 80 10 3.25 3.5, 3.75, 4, 4.25, 4.5, 4.75, 5, 5.25, 5.5, 5.75, 6, 6.25, 6.5, 6.75, 7, 7.25, 7.5, 7.75, 8, 8.25, 8.5, 8.75, 9, 9.25, 9.5, 9.75, 10, 10.25, 10.5, 10.75, 11, 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5, 19, 19.5, 20, 25, 30, 35, 40, 45, 50, 55, 60, 70, 80 11 3.5 3.75, 4, 4.25, 4.5, 4.75, 5, 5.25, 5.5, 5.75, 6, 6.25, 6.5, 6.75, 7, 7.25, 7.5, 7.75, 8, 8.25, 8.5, 8.75, 9, 9.25, 9.5, 9.75, 10, 10.25, 10.5, 10.75, 11, 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5, 19, 19.5, 20, 25, 30, 35, 40, 45, 50, 55, 60, 70, 80 12 3.75 4, 4.25, 4.5, 4.75, 5, 5.25, 5.5, 5.75, 6, 6.25, 6.5, 6.75, 7, 7.25, 7.5, 7.75, 8, 8.25, 8.5, 8.75, 9, 9.25, 9.5, 9.75, 10, 10.25, 10.5, 10.75, 11, 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5, 19, 19.5, 20, 25, 30, 35, 40, 45, 50, 55, 60, 70, 80 13 4 4.25, 4.5, 4.75, 5, 5.25, 5.5, 5.75, 6, 6.25, 6.5, 6.75, 7, 7.25, 7.5, 7.75, 8, 8.25, 8.5, 8.75, 9, 9.25, 9.5, 9.75, 10, 10.25, 10.5, 10.75, 11, 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5, 19, 19.5, 20, 25, 30, 35, 40, 45, 50, 55, 60, 70, 80 14 4.5 4.75, 5, 5.25, 5.5, 5.75, 6, 6.25, 6.5, 6.75, 7, 7.25, 7.5, 7.75, 8, 8.25, 8.5, 8.75, 9, 9.25, 9.5, 9.75, 10, 10.25, 10.5, 10.75, 11, 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5, 19, 19.5, 20, 25, 30, 35, 40, 45, 50, 55, 60, 70, 80 15 5 5.25, 5.5, 5.75, 6, 6.25, 6.5, 6.75, 7, 7.25, 7.5, 7.75, 8, 8.25, 8.5, 8.75, 9, 9.25, 9.5, 9.75, 10, 10.25, 10.5, 10.75, 11, 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5, 19, 19.5, 20, 25, 30, 35, 40, 45, 50, 55, 60, 70, 80 16 6 6.25, 6.5, 6.75, 7, 7.25, 7.5, 7.75, 8, 8.25, 8.5, 8.75, 9, 9.25, 9.5, 9.75, 10, 10.25, 10.5, 10.75, 11, 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5, 19, 19.5, 20, 25, 30, 35, 40, 45, 50, 55, 60, 70, 80 17 7 7.25, 7.5, 7.75, 8, 8.25, 8.5, 8.75, 9, 9.25, 9.5, 9.75, 10, 10.25, 10.5, 10.75, 11, 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5, 19, 19.5, 20, 25, 30, 35, 40, 45, 50, 55, 60, 70, 80 18 8 8.25, 8.5, 8.75, 9, 9.25, 9.5, 9.75, 10, 10.25, 10.5, 10.75, 11, 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5, 19, 19.5, 20, 25, 30, 35, 40, 45, 50, 55, 60, 70, 80 19 9 9.25, 9.5, 9.75, 10, 10.25, 10.5, 10.75, 11, 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5, 19, 19.5, 20, 25, 30, 35, 40, 45, 50, 55, 60, 70, 80 20 10 10.25, 10.5, 10.75, 11, 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5, 19, 19.5, 20, 25, 30, 35, 40, 45, 50, 55, 60, 70, 80 21 11 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5, 19, 19.5, 20, 25, 30, 35, 40, 45, 50, 55, 60, 70, 80 22 12 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5, 19, 19.5, 20, 25, 30, 35, 40, 45, 50, 55, 60, 70, 80 23 13 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5, 19, 19.5, 20, 25, 30, 35, 40, 45, 50, 55, 60, 70, 80 24 14 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5, 19, 19.5, 20, 25, 30, 35, 40, 45, 50, 55, 60, 70, 80 25 15 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5, 19, 19.5, 20, 25, 30, 35, 40, 45, 50, 55, 60, 70, 80

According to a further embodiment of this invention there is provided an all-vanadium redox battery/fuel cell having a positive compartment containing a catholyte in electrical contact with a catholyte contacting portion of a positive electrode, said catholyte contacting portion being disposed in said positive compartment, said positive electrode being selected from the group consisting of an oxygen electrode and an air electrode, the catholyte comprising an electrolyte solution containing vanadium ions selected from the group consisting of trivalent vanadium ions, tetravalent vanadium ions, pentavalent vanadium ions, and a mixture of at least two of trivalent vanadium ions, tetravalent vanadium ions, pentavalent vanadium ions, a negative compartment containing an anolyte in electrical contact with a negative electrode, the anolyte comprising an electrolyte solution containing vanadium ions selected from the group consisting of tetravalent vanadium ions, trivalent vanadium ions, divalent vanadium ions, and a mixture of at least two of trivalent vanadium ions, tetravalent vanadium ions, divalent vanadium ions, and a separator or membrane disposed between the positive and negative compartments and in contact with the catholyte and anolyte to provide ionic communication therebetween, at least one of the electrolyte solutions having the vanadium ions above 1.8M, more typically above 2M, even more typically above 2.5M or 3M, or typically above 5M, said positive electrode having a gas contacting portion said gas contacting portion being disposed so as to be capable of contacting a gas selected from the group consisting of oxygen, an oxygen containing gas, and air, and optionally means to maintain and/or control the operating temperature of the all-vanadium redox battery/fuel cell so as to substantially prevent or significantly reduce crystallisation or precipitation of vanadium substances/compounds from the at least one of the electrolyte solutions having the vanadium ions, typically above 20, more typically above 25° C. One or both of the electrolytes may optionally contain a stabilising amount of a stabilising agent.

According to a further embodiment of this invention there is provided an all-vanadium redox battery/fuel cell having a positive compartment containing a catholyte in electrical contact with a positive electrode, said positive electrode being disposed in said positive compartment, the catholyte comprising an electrolyte solution containing vanadium ions selected from the group consisting of trivalent vanadium ions, tetravalent vanadium ions, pentavalent vanadium ions, and a mixture of at least two of trivalent vanadium ions, tetravalent vanadium ions, pentavalent vanadium ions, a negative compartment containing an anolyte in electrical contact with an anolyte contacting portion of a negative electrode, said anolyte contacting portion being disposed in said negative compartment, said negative electrode being selected from the group consisting of a reducing gas electrode, a hydrogen gas electrode, the anolyte comprising an electrolyte solution containing vanadium ions selected from the group consisting of tetravalent vanadium ions, trivalent vanadium ions, divalent vanadium ions, and a mixture of at least two of trivalent vanadium ions, tetravalent vanadium ions, divalent vanadium ions, and a separator or membrane disposed between the positive and negative compartments and in contact with the catholyte and anolyte to provide ionic communication therebetween, at least one of the electrolyte solutions having a higher than 5M vanadium ions in at least one of the electrolyte solutions, said negative electrode having a gas contacting portion said gas contacting portion being disposed so as to be capable of contacting a gas selected from the group consisting of a reducing gas, a hydrogen containing gas, and hydrogen, and optionally means to maintain and/or control the operating temperature of the all-vanadium redox battery/fuel cell so as to substantially prevent or significantly reduce crystallisation or precipitation of vanadium substances/compounds from the at least one of the electrolyte solutions having the vanadium ions, typically above 20, more typically above 25° C. One or both of the electrolytes may optionally contain a stabilising amount of a stabilising agent.

Also disclosed is a process for the production of electricity from an all-vanadium redox battery/fuel cell of the invention when said battery/fuel cell is charged or partially charged, which process comprises withdrawing electrical energy from the redox battery/fuel cell by loading an external circuit in electronic communication with the positive and negative electrode.

Also disclosed are HED vanadium electrolyte solutions for use in an all-vanadium redox battery comprising vanadium redox ions V(II), V(III) and/or V(IV) ions above 1.8M, more typically above 2M, even more typically above 2.5M or 3M, or typically at 5M up to 10M or 20M, in the negative ½-cell of the battery and V(III), V(IV) and/or V(V) ions at above 1.8M, more typically above 2M, even more typically above 2.5M or 3M, or typically 5M up to 10M or 20M, in the positive ½-cell of the battery, each with a supporting aqueous electrolyte typically comprising 0.5–10M H₂SO₄.

Also disclosed are 1.801–10 or 3–10 or 5–10 molar, typically 5 molar, vanadium redox ion containing electrolyte solutions for use in an all-vanadium redox battery comprising vanadium redox ions V(II), V(III) and/or V(IV) ions at above saturated concentrations in the negative ½-cell and V(III), V(IV) and/or V(V) ions at above saturated concentrations in the positive ½-cell, each with a supporting electrolyte typically of 0.5–12M H₂SO₄.

Also disclosed are 5 molar vanadium electrolyte solutions for use in an all-vanadium redox battery comprising vanadium redox ions V(II), V(III) and/or V(IV) ions in the negative ½-cell and V(III), V(IV) and/or V(V) ions in the positive ½-cell, each with a supporting aqueous electrolyte typically of 0.5–10M H₂SO₄ and operating at a temperature above 25° C. which is sufficient to reduce precipitation of the vanadium redox ions from the HED electrolyte solution to a rate whereby the HED all-vanadium electrolyte solution is acceptable for use in an all-vanadium redox battery and in particular which is acceptable for long term stability on standing in the temperature range 25–70° C.

Also disclosed are 5–6 molar vanadium electrolyte solutions for use in an all-vanadium redox battery comprising vanadium redox ions V(II), V(III) and/or V(IV) ions in the negative ½-cell and V(III), V(IV) and/or V(V) ions in the positive ½-cell, each with a supporting aqueous electrolyte typically of 0.5–10M H₂SO₄ and operating at a temperature above 25° C. which is sufficient to reduce precipitation of the vanadium redox ions from the HED electrolyte solution to a rate whereby the HED all-vanadium electrolyte solution is acceptable for use in an all-vanadium redox battery and in particular is acceptable for long term stability on standing.

Also disclosed are 3–4 molar supersaturated vanadium electrolyte solutions for use in an all-vanadium redox battery comprising vanadium redox ions V(II), V(III) and/or V(IV) ions in the negative ½-cell and V(III), V(IV) and/or V(V) ions in the positive ½-cell, each with a supporting electrolyte typically of 0.5–10M H₂SO₄ and operating at a temperature above 25° C. which is sufficient to reduce precipitation of the vanadium redox ions from the HED electrolyte solution to a rate whereby the all-vanadium electrolyte solution is acceptable for use in an all-vanadium redox battery.

Also disclosed are 4–5 molar supersaturated vanadium electrolyte solutions for use in an all-vanadium redox battery comprising vanadium redox ions V(II), V(III) and/or V(IV) ions in the negative ½-cell and V(III), V(IV) and/or V(V) ions in the positive ½-half cell, each with a supporting electrolyte typically of 0.5–10M H₂SO₄ and operating at a temperature above 25° C. which is sufficient to reduce precipitation of the vanadium redox ions from the HED electrolyte solution to a rate whereby the all-vanadium electrolyte solution is acceptable for use in an all-vanadium redox battery.

Also disclosed are 2–12, more typically 3–12, more typically 5–12 molar supersaturated vanadium electrolyte solutions for use in an all-vanadium redox battery comprising vanadium redox ions V(II), V(III) and/or V(IV) ions in the negative ½-cell and V(III), V(IV) and/or V(V) ions in the positive ½-cell, each with a supporting aqueous electrolyte typically of 0.5–12M H₂SO₄ and an operating temperature above 25° C. which is sufficient to reduce precipitation of the vanadium redox ions from the HED electrolyte solution to a rate whereby the HED all-vanadium electrolyte solution is acceptable for use in an all-vanadium redox battery.

Also disclosed are supersaturated vanadium electrolytes for use in an all-vanadium redox battery comprising supersaturated vanadium redox ions V(II), V(III) and/or V(IV) ions in the negative ½-cell and V(III), V(IV) and/or V(V) ions in the positive ½-cell, each with a supporting aqueous electrolyte typically of 0.5–12M H₂SO₄ (or total sulphate) and an operating temperature above 25° C. which is sufficient to reduce precipitation of the vanadium redox ions from the HED electrolyte solution to a rate whereby the HED all-vanadium electrolyte solution is acceptable for use in an all-vanadium redox battery and in particular to reduce precipitation of the vanadium ions from the HED supersaturated vanadium electrolyte solution to a rate which is acceptable for long term stability on standing.

Also disclosed is a process for making HED supersaturated electrolyte solution by electrolytic oxidation of a suspension of V₂O₃ and/or V₂O₄ and/or VOSO₄ powder to produce V(V) ions at above 1.8M, more typically above 2M, even more typically above 2.5M or 3M, or typically from 5M up to and including a supersaturated concentration at the anode of an electrolysis cell containing a supporting aqueous electrolyte typically of 0.5–12M H₂SO₄ (or total sulphate). The V(II), V(III) and V(IV) redox ions are produced by reduction of V(V) in solution at up to and including a supersaturated concentration.

Also disclosed is a process for making HED supersaturated electrolyte solution by electrolytic reduction of V₂O₅ suspension at the cathode of an electrolysis cell containing supporting aqueous electrolyte typically of 0.5–12M H₂SO₄ (or total sulphate) and reducing for sufficient time to produce a 50:50 mixture of V(III) and V(IV) (V^(3.5+)) which is then placed into both sides of the vanadium redox battery (“VRB”) and charged to V(II) and V(V) states respectively or left in discharged form of V(III) and V(IV) respectively until needed.

Also disclosed is a process for making HED supersaturated V^(3.5+) electrolyte solution by concentrating a 2M V^(3.5+) solution.

Also disclosed is a process for making V^(3.5+) electrolyte concentrate (as suspended slurry) by the process for making HED supersaturated V^(3.5+) electrolyte solution, by concentrating a 2M V^(3.5+) solution by boiling or pervaporation or applying vacuum and/or heat to remove the required amount of water and reconstituting by adding the required amount of water to redissolve vanadium precipitate to form a supersaturated solution just prior to addition to vanadium redox battery electrolyte solution tanks.

The vanadium redox ions may be above 1.8M, more typically above 2M, even more typically above 2.5M or 3M, or typically 5M up to 10M or 20M. Typically the negative and positive compartments are sealed air-tight. Optionally the negative and positive compartments are deaerated. Typically the negative electrolyte solution is covered with a blanket of inert oil to oxidise air.

All-vanadium redox charge and discharge cells of the invention can be operated over a broad temperature range, e.g. 25° C. to 99° C. or 30° C. to 99° C. but are typically operated in the temperature range 25° C. to 65° C. or 30° C. to 65° C., 30° C. to 50° C.,

The means to maintain and/or control the operating temperature of the all-vanadium redox battery or redox battery/fuel cell, so as to substantially prevent or significantly reduce crystallisation or precipitation of vanadium substances/compounds from the catholyte and/or anolyte, may be any suitable heating and/or cooling and/or insulating means, e.g. a hotplate, hot water or steam jacket, hot gas jacket (heated with, for example, hot gas exhausted from a car engine or solar heated hot air), heating mantle, electrical heater, heat exchanger (including a solar heat exchanger such as a solar hot water heat exchanger), or a gas flame (such as a flame from a Bunsen burner or from a natural gas burner) or polystyrene insulation.

In the methods and processes of the invention for forming a HED solution of vanadium ions, initially a viscous HED solution is generally formed (which may be a colloidal particle/solution mixture) of vanadium ions (typically >3M vanadium ions, typically 3.01M–10M, more typically 5.01M–6.5M). The viscous HED solution is then typically maintained, with or without stirring, at room temperature for about 2 weeks to a month or more, or at 25–99° C., typically 25–95° C. for 0.1 day–30 days, typically 0.5 day–20 days, until its viscosity substantially decreases. The V(II), V(III) and V(IV) ions in the HED solution, before or after reducing the viscosity of the HED solution, may be reduced to form a solution of V(II)/V(III) ions or oxidised to form a solution of V(IV)/V(V) ions. Advantageously the viscous HED solution/colloidal particle mixture is maintained at a temperature or temperature range e° C.–f° C. where e is selected from the group consisting of a value presented in the column headed “e” in Table B at one of entries 1–10, and f is selected from the group of the values presented in the column headed “f” adjacent the corresponding “e” entry to substantially reduce or prevent crystallisation or precipitation of vanadium substances/compounds for a time in the range selected from the group consisting of w days to x days, where w is selected from the group consisting of a value presented in the column headed “w” in Table F below at one of entries 1–25, and x is selected from the group of the values presented in the column headed “x” adjacent the corresponding “w” entry.

TABLE F Entry w x 1 1 1.25, 1.5, 1.75, 2, 2.25, 2.5, 2.75, 3, 3.25, 3.5, 3.75, 4, 4.25, 4.5, 4.75, 5, 5.25, 5.5, 5.75, 6, 6.25, 6.5, 6.75, 7, 7.25, 7.5, 7.75, 8, 8.25, 8.5, 8.75, 9, 9.25, 9.5, 9.75, 10, 10.25, 10.5, 10.75, 11, 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5, 19, 19.5, 20, 25, 30, 35, 40, 45, 50 , 55, 60, 70, 80 2 1.25 1.5, 1.75, 2, 2.25, 2.5, 2.75, 3, 3.25, 3.5, 3.75, 4, 4.25, 4.5, 4.75, 5, 5.25, 5.5, 5.75, 6, 6.25, 6.5, 6.75, 7, 7.25, 7.5, 7.75, 8, 8.25, 8.5, 8.75, 9, 9.25, 9.5, 9.75, 10, 10.25, 10.5, 10.75, 11, 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5, 19, 19.5, 20, 25, 30, 35, 40, 45, 50, 55, 60, 70, 80 3 1.5 1.75, 2, 2.25, 2.5, 2.75, 3, 3.25, 3.5, 3.75, 4, 4.25, 4.5, 4.75, 5, 5.25, 5.5, 5.75, 6, 6.25, 6.5, 6.75, 7, 7.25, 7.5, 7.75, 8, 8.25, 8.5, 8.75, 9, 9.25, 9.5, 9.75, 10, 10.25, 10.5, 10.75, 11, 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5, 19, 19.5, 20, 25, 30, 35, 40, 45, 50, 55, 60, 70, 80 4 1.75 2, 2.25, 2.5, 2.75, 3, 3.25, 3.5, 3.75, 4, 4.25, 4.5, 4.75, 5, 5.25, 5.5, 5.75, 6, 6.25, 6.5, 6.75, 7, 7.25, 7.5, 7.75, 8, 8.25, 8.5, 8.75, 9, 9.25, 9.5, 9.75, 10, 10.25, 10.5, 10.75, 11, 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5, 19, 19.5, 20, 25, 30, 35, 40, 45, 50, 55, 60, 70, 80 5 2 2.25, 2.5, 2.75, 3, 3.25, 3.5, 3.75, 4, 4.25, 4.5, 4.75, 5, 5.25, 5.5, 5.75, 6, 6.25, 6.5, 6.75, 7, 7.25, 7.5, 7.75, 8, 8.25, 8.5, 8.75, 9, 9.25, 9.5, 9.75, 10, 10.25, 10.5, 10.75, 11, 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5, 19, 19.5, 20, 25, 30, 35, 40, 45, 50, 55, 60, 70, 80 6 2.25 2.5, 2.75, 3, 3.25, 3.5, 3.75, 4, 4.25, 4.5, 4.75, 5, 5.25, 5.5, 5.75, 6, 6.25, 6.5, 6.75, 7, 7.25, 7.5, 7.75, 8, 8.25, 8.5, 8.75, 9, 9.25, 9.5, 9.75, 10, 10.25, 10.5, 10.75, 11, 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5, 19, 19.5, 20, 25, 30, 35, 40, 45, 50, 55, 60, 70, 80 7 2.5 2.75, 3, 3.25, 3.5, 3.75, 4, 4.25, 4.5, 4.75, 5, 5.25, 5.5, 5.75, 6, 6.25, 6.5, 6.75, 7, 7.25, 7.5, 7.75, 8, 8.25, 8.5, 8.75, 9, 9.25, 9.5, 9.75, 10, 10.25, 10.5, 10.75, 11, 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5, 19, 19.5, 20, 25, 30, 35, 40, 45, 50, 55, 60, 70, 80 8 2.75 3, 3.25, 3.5, 3.75, 4, 4.25, 4.5, 4.75, 5, 5.25, 5.5, 5.75, 6, 6.25, 6.5, 6.75, 7, 7.25, 7.5, 7.75, 8, 8.25, 8.5, 8.75, 9, 9.25, 9.5, 9.75, 10, 10.25, 10.5, 10.75, 11, 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5, 19, 19.5, 20, 25, 30, 35, 40, 45, 50, 55, 60, 70, 80 9 3 3.25, 3.5, 3.75, 4, 4.25, 4.5, 4.75, 5, 5.25, 5.5, 5.75, 6, 6.25, 6.5, 6.75, 7, 7.25, 7.5, 7.75, 8, 8.25, 8.5, 8.75, 9, 9.25, 9.5, 9.75, 10, 10.25, 10.5, 10.75, 11, 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5, 19, 19.5, 20, 25, 30, 35, 40, 45, 50, 55, 60, 70, 80 10 3.25 3.5, 3.75, 4, 4.25, 4.5, 4.75, 5, 5.25, 5.5, 5.75, 6, 6.25, 6.5, 6.75, 7, 7.25, 7.5, 7.75, 8, 8.25, 8.5, 8.75, 9, 9.25, 9.5, 9.75, 10, 10.25, 10.5, 10.75, 11, 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5, 19, 19.5, 20, 25, 30, 35, 40, 45, 50, 55, 60, 70, 80 11 3.5 3.75, 4, 4.25, 4.5, 4.75, 5, 5.25, 5.5, 5.75, 6, 6.25, 6.5, 6.75, 7, 7.25, 7.5, 7.75, 8, 8.25, 8.5, 8.75, 9, 9.25, 9.5, 9.75, 10, 10.25, 10.5, 10.75, 11, 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5, 19, 19.5, 20, 25, 30, 35, 40, 45, 50, 55, 60, 70, 80 12 3.75 4, 4.25, 4.5, 4.75, 5, 5.25, 5.5, 5.75, 6, 6.25, 6.5, 6.75, 7, 7.25, 7.5, 7.75, 8, 8.25, 8.5, 8.75, 9, 9.25, 9.5, 9.75, 10, 10.25, 10.5, 10.75, 11, 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5, 19, 19.5, 20, 25, 30, 35, 40, 45, 50, 55, 60, 70, 80 13 4 4.25, 4.5, 4.75, 5, 5.25, 5.5, 5.75, 6, 6.25, 6.5, 6.75, 7, 7.25, 7.5, 7.75, 8, 8.25, 8.5, 8.75, 9, 9.25, 9.5, 9.75, 10, 10.25, 10.5, 10.75, 11, 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5, 19, 19.5, 20, 25, 30, 35, 40, 45, 50, 55, 60, 70, 80 14 4.5 4.75, 5, 5.25, 5.5, 5.75, 6, 6.25, 6.5, 6.75, 7, 7.25, 7.5, 7.75, 8, 8.25, 8.5, 8.75, 9, 9.25, 9.5, 9.75, 10, 10.25, 10.5, 10.75, 11, 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5, 19, 19.5, 20, 25, 30, 35, 40, 45, 50, 55, 60, 70, 80 15 5 5.25, 5.5, 5.75, 6, 6.25, 6.5, 6.75, 7, 7.25, 7.5, 7.75, 8, 8.25, 8.5, 8.75, 9, 9.25, 9.5, 9.75, 10, 10.25, 10.5, 10.75, 11, 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5, 19, 19.5, 20, 25, 30, 35, 40, 45, 50, 55, 60, 70, 80 16 6 6.25, 6.5, 6.75, 7, 7.25, 7.5, 7.75, 8, 8.25, 8.5, 8.75, 9, 9.25, 9.5, 9.75, 10, 10.25, 10.5, 10.75, 11, 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5, 19, 19.5, 20, 25, 30, 35, 40, 45, 50, 55, 60, 70, 80 17 7 7.25, 7.5, 7.75, 8, 8.25, 8.5, 8.75, 9, 9.25, 9.5, 9.75, 10, 10.25, 10.5, 10.75, 11, 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5, 19, 19.5, 20, 25, 30, 35, 40, 45, 50, 55, 60, 70, 80 18 8 8.25, 8.5, 8.75, 9, 9.25, 9.5, 9.75, 10, 10.25, 10.5, 10.75, 11, 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5, 19, 19.5, 20, 25, 30, 35, 40, 45, 50, 55, 60, 70, 80 19 9 9.25, 9.5, 9.75, 10, 10.25, 10.5, 10.75, 11, 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5, 19, 19.5, 20, 25, 30, 35, 40, 45, 50, 55, 60, 70, 80 20 10 10.25, 10.5, 10.75, 11, 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5, 19, 19.5, 20, 25, 30, 35, 40, 45, 50, 55, 60, 70, 80 21 11 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5, 19, 19.5, 20, 25, 30, 35, 40, 45, 50, 55, 60, 70, 80 22 12 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5, 19, 19.5, 20, 25, 30, 35, 40, 45, 50, 55, 60, 70, 80 23 13 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5, 19, 19.5, 20, 25, 30, 35, 40, 45, 50, 55, 60, 70, 80 24 14 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5, 19, 19.5, 20, 25, 30, 35, 40, 45, 50, 55, 60, 70, 80 25 15 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5, 19, 19.5, 20, 25, 30, 35, 40, 45, 50, 55, 60, 70, 80

The anolyte and the catholyte comprise an electrolyte which is typically an aqueous solution which includes at least one of H₂O₄, trifluoromethanesulphonic acid, Na₂SO₄, ammonium sulphate, K₂SO₄, H₃PO₄, Na₃PO₄, K₃PO₄, KNO3, NaNO₃, sulphonic acid, C₆–C₁₄ arylsulphonic acid such as p-toluenesulphonic acid, benzenesulphonic acid, naphthlenesulphonic acid, C₁–C₆ alkylsulphonic acid such as methylsulphonic acid and ethylsulphonic acid, acetic acid or mixtures thereof in a concentration of from 0.01M to 20M, or 0.01M to 15M, 0.01M to 10M. It is especially preferred to use H₂SO₄ (alternatively expressed as total sulphate concentration) in a concentration of from 1.5M to 10M, more preferably 1.75M to 10M (other concentration ranges include 0.25M to 10M, 2M to 10M, 2M to 9M, 2.5M to 9M, 2.8M to 8M, 3M to 7M, 3M to 6M, 4M to 6.5M, 5.001M to 10M, 5.001M to 7.5M, 5.001M to 10M, 5.001M to 7.0M, and 5.001M to 6M) H₂SO₄ (or total sulphate). It is especially preferred to use H₂SO₄ (alternatively expressed as total sulphate concentration) in a concentration of from 2M to 9M, more preferably 4.5M to 9M.

The electrolyte solution typically has vanadium ions V(II), V(III), V(IV) and/or V(V) ions in any form, (examples of forms include vanadate ions such as metavanadate, orthovanadate, pyrovanadate, as well as vanadyl ions such as vanadylous and divalent vanadyl ions) in sufficient concentration for high discharge capacity in the discharge battery, for example, up to and including a supersaturated concentration, 1.801M to 15M, 3M to 15M, 5.001 to 15M, 5.1M to 12M, 5.25M to 10M, 5M to 10M, 5M to 9M, 5.5M to 9M, 5M to 8M, 5M to 7M, 5M to 6M, 5.001M to 10M, 5.001M to 7.5M, 5.001M to 10M, 5.001M to 7.0M, and 5.001M to 6M, 3M to 7M or 3M to 6M are typical in the charge and discharge cells of the invention. The vanadium ions in the electrolyte solution are prepared by dissolving an oxide, sulphate, phosphate, nitrate, halogenide or other salt or complex of vanadium which is soluble or which can be solubilized in the electrolyte solution. Examples of suitable vanadium salts include ammonium metavanadate (NH₄VO₃); ammonium vanadium sulphate (NH₄V(SO₄)₂); barium pyrovanadate (Ba₂V₂O₇); bismuth vanadate (Bi₂O₃ V₂O₅); cesium vanadium sulphate (VCs(SO₄)₂ 12H₂O); iron metavanadate (Fe(VO₂)₃); lead metavanadate (Pb(VO₅)₂); potassium metavanadate (KVO₃); potassium vanadium sulphate (KVSO₄); rubidium vanadium sulphate (RbV(SO₄)₂); sodium metavanadate (NaVO₃); metavanadic acid (HVO₃); sodium orthovanadate (Na₃VO₄); potassium orthovanadate (K₃VO₄); ammonium orthovanadate; sodium pyrovanadate (Na₄V₂O₇); potassium pyrovanadate (K₄V₂O₇); ammonium pyrovanadate; sodium hexavanadate (Na₄V₆O₁₇); potassium hexavanadate (K₄V₆O₁₇); ammonium hexavanadate; thallium pyrovanadate (Tl₄V₂O₇); thallium metavanadate (TlVO₃); thallium pyrovanadate (TlV₂O₇ 6H₂O); vanadium pentoxide (V₂O₅); vanadium sulphate (V(SO₄)₂); vanadium sulphate (V₂(SO₄)₂); vanadium oxide VO; and calcium and magnesium vanadates including calcium metavanadate and magnesium metavanadate. Other vanadium salts and complexes can also be dissolved and reduced in an electrolyte solution. Generally for an all-vanadium redox battery, the catholyte and anolyte include a solution of vanadium prepared from a salt selected from the group consisting of a salt of the formula VO(X)_(y) where y is 2 and X is F, Br or Cl, a salt of the formula VO(X)_(y) where y is 1 and X is SO₄ or O, V₂O₅, V₂O₃, V₂O₄, VSO₄, V₂(SO₄)₃, (VO₂)₂SO₄, and NH₄VO₃. Vanadium salts or complexes such as ammonium metavanadate (NH₄VO₃), V₂O₅, V₂O₃, V₂O₄, VSO₄, V₂(SO₄)₃, VOSO₄ and ammonium vanadium sulphate (NH₄V(SO₄)₂) are particularly advantageous since no additional ions other than vanadium sulphate and ammonium are introduced permitting higher concentrations of vanadium ions to be prepared and reducing further treatment of electrolyte solution to remove unwanted products. It is especially preferable to dissolve vanadyl sulphate in 1M to 10M, more typically 1 to 9M, and even more typically 1 to 8M and yet even more typically 1 to 7.5M H₂SO₄ or V₂O₅ or ammonium metavanadate in 3M to 12M, more typically 3 to 10M, and even more typically 3 to 10M and yet even more typically 5 to 7.5M H₂SO₄ by electrolytic dissolution or by chemical leaching with V(III) or other suitable reductant (see e.g. International Application No. PCT/AU88/00471 the contents of which are incorporated herein by cross reference).

The cells and batteries of the invention may be constructed according to generally known methods for construction of redox cells.

The electrochemical reactions of the redox cell can be conducted in any electrochemical cell which has an anode compartment and a cathode compartment through which the appropriate fluids can be transported.

The electrochemical cell is typically a cell of the “membrane-type”, that is it employs a membrane rather than a diaphragm to separate a positive compartment from a negative compartment. The membrane employed is typically sheet-like and can transport electrolyte ions whilst at the same time being hydraulically-impermeable in contrast to a diaphragm (typically asbestos) which allows restricted electrolyte transfer between compartments. Thus the separator can be a microporous separator or a ionically conducting membrane fabricated from a polymer based on perfluorocarboxylic acids or a proton exchange polymer such as sulphonated polystyrene, sulphonated polyethylene or a substantially fluorinated sulphonic acid polymer such as Naflon (Trade Mark) or membranes of Flemion (Trade Mark), Selemion (Trade Mark) or New Selemion (Trade Mark) material as manufactured by Asahi Glass Company. Other suitable membranes are as disclosed in International Application No. PCT/AU92/00491, the contents of which are incorporated herein by cross reference.

Although the design of the anode and cathode compartments of the redox cell are not critical to the practice of this invention, certain embodiments are preferred. For example, a parallel plate electrochemical cell in which anode and cathode compartments alternate in order to increase voltage and decrease current is a preferred embodiment. The configuration of the cell may be such that there are intermediate bipolar electrodes between end plate electrodes. The electrode material will depend on the nature and composition of the anolytes and catholytes in the redox cell and are typically chosen on efficiency and stability grounds, i.e. the higher the efficiency and the greater stability in the particular anolyte and catholyte used in the redox battery, then generally the more it is favoured. Typical positive and negative electrodes may be metal, or carbon/graphite, as described in International Patent Application No. PCT/AU93/00456 incorporated herein by cross reference, glassy (amorphous) carbons, reticulated vitreous carbons, pyrolytic carbons, carbon and graphite felt, mat, plate, rod, knit, fibre, and cloth; carbon impregnated teflon; carbon impregnated polyethylene; carbon impregnated polypropylene; carbon impregnated polystyrene; carbon impregnated polyvinylchloride; carbon impregnated polyvinylidenechloride; glassy carbon; non-woven carbon fibre material; cellulose; carbon and graphite felt, mat, plate, rod, knit, fibre, and cloth, carbon impregnated teflon, carbon impregnated polyethylene, carbon impregnated polypropylene, carbon impregnated polystyrene, carbon impregnated polyvinylchloride and carbon impregnated polyvinylidenechloride, impregnated with and/or coated with Au, Pt, Ir, Ru, Os, Re, Rh and/or Ag; platinised Ti; platinised Ru; platinised Ir; platinised Pd; Pt; Pt black; dimensionally stabilized anode (DSA) (Ti or Ti alloy core, coated at least partially with titanium dioxide which coating is coated or doped in turn with a noble metal coating selected from the group consisting of Pt, Pd, Os, Rh, Ru, Ir and alloys thereof); Au; Pd; Ir; Ru; Os; Re; Rh; Hg; Ag; Tl; Bi; Pb; In; Cd; Ga; Sb; Zn; Pb/Hg; Pb/Bi; Hg/In; Hg/Cd; or Hg/Ga or other suitable electrodes. Generally, carbon/graphite electrodes such as glassy (amorphous) carbons, reticulated vitreous carbons, pyrolytic carbons, carbon and graphite felt, mat, plate, rod, knit, fibre, and cloth; are bonded onto a conducting substrate such as carbon impregnated teflon, carbon impregnated polyethylene, carbon impregnated polypropylene, carbon impregnated polystyrene, carbon impregnated polyvinylchloride and carbon impregnated polyvinylidenechloride, etc.

The construction of the electrode will depend on the material type, with metal electrodes generally being in the form of plates, bars, and screens, or being sintered to form a highly porous structure. The positive and negative electrodes can be any shape desired. It is preferred that the positive and negative electrodes are rectangular-plate shaped. Metal electrodes may also be formed by depositing a film or layer of the metal on a nonconductive substrate, such as glass. The structure of carbon/graphite electrodes will depend upon the type of carbon. Glassy carbon electrodes are generally flat, polished surfaces while reticulated vitreous carbons are glass-like porous structures, typically pyrolyzed polyacrylonitriles. Pyrolytic carbons are produced by vapour phase deposition of carbon on a substrate, resulting in a polycrystalline structure with a high degree of atomic orientation. Preferred is the use of graphite, carbon/graphite or carbon felt electrodes which have been found to provide particularly effective catalytic sites after an oxidation pretreatment. The graphite, carbon/graphite or carbon felt electrodes are generally bonded onto a conducting carbon or graphite filled plastic electrode to form the final electrode configuration (see International Patent Application No. PCT/AU93/00456 incorporated herein by cross reference). Carbon felts are generally woven from yarns which are bundles of individual carbon monofilaments generally having a diameter in the range from about 1 to 50 μm, usually in the range from about 5 to 10 μm. The yarns will typically include from about 100 to 20,000 monofilaments, usually having from about 3,000 to 6,000 filaments. The denier of the yarns used as in fabricating the carbon felts will typically be in the range from about 500 to 5,000 mg/m, usually being in the range from about 1,000 to 2,000 mg/m. Denier is equal to the number of grams which yield 9,000 meters of the yam or filament. The yams are woven by conventional weaving machines yielding large fabrics which may be cut into the desired dimensions for the electrode. Each electrode may employ a plurality of layers of the fabric, so that the final dimensions of the electrode may vary widely. Generally, the electrodes will have a height in the range from about 0.5 cm to 2 metres, more typically, 5 to 1000 cm, a width in the range from about 0.1 cm to 2 metres, more typically, 5 to 1000 cm, and a thickness in the range from about 0.1 cm to 1.0 cm. The particular dimensions chosen will depend primarily on the power output of the electrochemical cell. Carbon felts suitable for use in the present invention may be obtained commercially from suppliers such as FMI Fibre Materials, Inc., Biddleford, Me.; Hercules, Inc., Wilmington, Del.; Celanese Engineering, Chatham, N.J.; Ultra Carbon Corp., Bay City, Mich.; and Union Carbide Corp., Mitsubishi, Japan, Toray, Japan, Kureha, Toyoba, Japan, Sigri, Germany, Specialty Polymers and Composites Division, Danbury, Conn.

The redox cell includes monopolar and bipolar type discharge cells, charge cells or charge/discharge cells. A bipolar discharge cell typically includes a plurality of positive discharge compartments each having a positive discharge electrode therein and a plurality of negative discharge compartments each having a negative discharge electrode therein and wherein each of the compartments are separated by a membrane. A bipolar discharge cell is typically of the flat plate-or filter press-type.

For other methods of dissolving V₂O₅ and other vanadium salts are disclosed below.

According to another embodiment of this invention there is provided a process for producing a HED vanadium electrolyte solution, of above 1.8M, typically 3M up to and including supersaturated concentration, by dissolving and reducing a reducible vanadium compound disposed in, but not wholly dissolved in, an aqueous electrolyte by utilizing an electrochemical cell which aqueous electrolyte is in electrical contact with a positive electrode and a negative electrodes to dissolve and reduce at least a part of the compound in the electrolyte solution.

According to another embodiment of this invention there is provided a process for producing a HED vanadium electrolyte solution, of above 1.8M, typically 3M up to and including supersaturated concentration, by dissolving and reducing a reducible vanadium compound disposed in, but not wholly dissolved in, an aqueous electrolyte by utilizing an electrochemical cell having a positive compartment containing a catholyte in electrical contact with a positive electrode, a negative compartment containing an anolyte comprising an aqueous electrolyte in electrical contact with a negative electrode, and an ionically conducting separator disposed between the positive and negative compartments and in contact with the catholyte and the anolyte to provide ionic communication therebetween which process comprises adding the vanadium compound to the aqueous electrolyte or wherein the vanadium compound is predisposed in the aqueous electrolyte, and providing electrical energy from an external circuit to the positive and negative electrodes to dissolve and reduce at least a part of the compound in the aqueous electrolyte.

The aqueous electrolyte can include vanadium (II) and/or vanadium (III) ions predisposed therein. The vanadium compound is thus reduced and dissolved by the V(II)/V(III) ions in addition to the aqueous solution and resultant V(IV) ions can be reduced at the negative electrode to V(II)/V(III) ions. Generally above saturated concentrations, or above 1.801M to supersaturated concentration, above 2M to supersaturated concentration, or 3M to 15M, or 5.1 to 15M, or 5.05 to 10M typically 5.25M to 8M or 3M to 8M V(II)/V(III) ions are included in the aqueous electrolyte. By V(II)/V(III) is meant V(II) ions alone or V(III) alone or a mixture of V(II) and V(III) ions.

According to another embodiment of this invention there is provided a process for producing a HED vanadium electrolyte solution, of above saturated concentration, by dissolving and reducing a reducible vanadium compound disposed in, but not wholly dissolved in, an aqueous electrolyte which process comprises adding a chemical reductant to the electrolyte solution to dissolve and reduce the compound in the electrolyte solution.

According to another embodiment of this invention there is provided a process for producing a HED vanadium electrolyte solution, of above saturated concentration, by dissolving and reducing a reducible vanadium compound disposed in, but not wholly dissolved in, an aqueous electrolyte by utilizing a chemical reductant and an electrochemical cell having the aqueous electrolyte in electrical contact with a positive electrode and a negative electrode which process comprises:

(a) adding a chemical reductant to the electrolyte solution to assist in dissolution and reduction of the compound in the electrolyte solution; and

(b) providing electrical energy from an external circuit to the positive and negative electrodes to dissolve and reduce at least a part of the compound in the electrolyte solution.

According to another embodiment of this invention there is provided a process for producing a HED vanadium electrolyte solution, of 1.801M, typically 3M up to and including supersaturated concentration, by dissolving and reducing a reducible vanadium compound disposed in, but not wholly dissolved in, an aqueous electrolyte by utilizing a chemical reductant and an electrochemical cell having a positive compartment containing a catholyte in electrical contact with a positive electrode, a negative compartment containing an anolyte comprising the aqueous electrolyte in electrical contact with a negative electrode, and an ionically conducting separator disposed between the positive and negative compartments and in contact with the catholyte and the anolyte to provide ionic communication therebetween which process comprises:

(a) adding a chemical reductant to the anolyte to assist in dissolution and reduction of the compound in the anolyte; and

(b) providing electrical energy from an external circuit to the positive and negative electrodes to dissolve and reduce at least a part of the compound in the electrolyte solution.

Alternative processes for the preparation of a HED vanadium electrolyte solution, optionally highly supersaturated with vanadium ions can be performed by adapting the processes described in AU85862/91, the contents of which are incorporated by cross reference.

The chemical reductant can be a V(II), V(III) or V(IV) compound, which is soluble in the electrolyte solution or an aqueous solution containing V(II), V(III) and/or V(IV) ions, particularly an aqueous solution of VOSO₄.dihydrate, hydrated (V₂(SO₄)₃) and/or VSO₄.7H₂O, in an amount sufficient to dissolve and reduce the vanadium compound. It is particularly preferred that a V(II) or V(III) compound, or the aqueous solution contains V(II) and/or V(III) ions. Even more preferable is that a V(III) compound is used as a reductant for V₂O₅ or NH₄VO₃.

The chemical reductant may also be KHC₂O₄.H₂O, K₂C₂O₄, Na₂C₂O₄, (NH₄)₂C₂O₄NH₄HC₂O₄.H₂O, LiHC₂O₄.H₂O, NaHC₂O₄.H₂O, Li₂C₂O₄, SO₂, H₂C₂O₄, H₂SO₃, NaHSO₃, Na₂SO₃, Na₂S₂O₃, Na₂S₂O₄, Na₂S₂O₅, Na₂S₂O₆, Li₂SO₃, Li₂SO₆, KHSO₃, K₂SO₃, K₂S₂O₃, K₂S₂O₄, K₂S₂O₅, K₂S₂O₆, NH₄HSO₃, (NH₄)₂SO₃, (NH₄)₂SO₄, (NH₄)₂SO₅, N₂H₄, H₂N₂H₂.H₂O, H₂N₂H₂.H₂SO₄, (NH₄)₂SO₆, NaBH₄, LiBH₄, KBH₄, Be(BH₄)₂, D₂, T₂, S, H₂O₂, hydrazine, sulphurous acid, hydrazine dihydrochloride, hydrogen peroxide, CaH₂, MgH₂, H₂ or calcium and magnesium salts of sulphurous acid, alkali-hydrogen-phosphites (Li, K, Na), alkali hypophosphites (Li, K, Na), hydroxyl amines, pyrosulphurous acid and dithioneous acid. Other chemical reductants can be used. For example, in principle it should possible to use a reducing organic water-soluble compound such as a reducing organic water-soluble mercapto group-containing compound including SH-containing water-soluble lower alcohols (including SH-containing C₁–C₁₂ primary, secondary and tertiary alkyl alcohols), SH-containing C₁–C₁₂ primary, secondary and tertiary alkyl carboxylic acids, SH-containing C₁–C₁₂ primary, secondary and tertiary alkyl amines and salts thereof, SH-containing C₁–C₁₂ primary, secondary and tertiary alkyl amine acids and di or tripeptides such as 2-mercaptoethylamine hydrochloride, 2-mercaptoethanol, 2-mercaptopropionylglycine, 2-mercaptopropionic acid, cystenylglycine, cysteine, carbamoyl cysteine, homocysteine, glutathione, cysteine hydrochloride ethyl ester and acetylcysteine. In principle it should also be possible to employ photocatalytic reduction and photoreduction at a semiconductor photocathode.

Reductants such as (NH₄)₂C₂O₄NH₄HC₂O₄.H₂O, SO₂, S, H₂O₂, H₂C₂O₄, NH₄HSO₃, (NH₄)₂SO₃, (NH₄)₂SO₄, (NH₄)₂SO₅, N₂H₄, H₂N₂H₂.H₂O, H₂N₂H₂.H₂SO₄, (NH₄)₂SO₆ and H₂ are particularly advantageous since at least some of the reaction product is gaseous permitting higher concentrations of vanadium ions to be prepared and reducing further treatment of electrolyte solution to remove unwanted products.

The vanadium compound can be ammonium metavanadate (NH₄VO₃); ammonium vanadium sulphate (NH₄V(SO₄)₂); barium pyrovanadate (Ba₂V₂O₇); bismuth vanadate (Bi₂O₃ V₂O₅); cesium vanadium sulphate (VCs(SO₄)₂ 12H₂O); iron metavanadate (Fe(VO₂)₃); lead metavanadate (Pb(VO₅)₂); potassium metavanadate (KVO₃); potassium vanadium sulphate (KVSO₄); rubidium vanadium sulphate (RbV(SO₄)₂); sodium metavanadate (NaVO₃); metavanadic acid (HVO₃); sodium orthovanadate (Na₃VO₄); sodium pyrovanadate (Na₄V₂O₇); sodium hexavanadate (Na₄V₆O₁₇); thallium pyrovanadate (Tl₄V₂O₇); thallium metavanadate (TlVO₃); thallium pyrovanadate (TlV₂O₇ 6H₂O); vanadium pentoxide (V₂O₅); vanadium sulphate (V(SO₄)₂); V₂O₃, V₂O₄, VO₂, VO and calcium and magnesium vanadates including calcium metavanadate and magnesium metavanadate. Other vanadium salts and complexes can also be dissolved and reduced in an electrolyte solution by the processes of the invention. For example, in principle it should also be possible to produce highly supersaturated HED vanadium electrolyte solutions by dissolving and reducing vanadium salts occurring in vanadium-bearing minerals such as patronite, bravoite, sulvanite, davidite, roscoelite, carnotite, vanadinite, descloizite, cuprodescloizite, vanadiferous phosphate rock and titaniferous magnetite using the processes of the invention as well as for recovering vanadium from spent catalysts and fly-ash.

Vanadium salts or complexes such as ammonium metavanadate (NH₄VO₃), VOSO₄, and ammonium vanadium sulphate (NH₄V(SO₄)₂), V₂O₅, V₂O₃, V₂O₄, VO₂, are particularly advantageous since they permit higher concentrations of vanadium ions to be prepared and reduce further treatment of electrolyte solution to remove unwanted products.

Supersaturated vanadium electrolyte solutions can also be prepared by adding V(II), V(III) or V(IV) compounds to a solution containing V(V) ions which act as an oxidising agent to oxidise and dissolve the normally insoluble vanadium compound. For example, V₂O₃ can be dissolved by a V(V) solution to produce a supersaturated V(IV) solution. The electrolyte typically comprises an aqueous solution which includes H₂SO₄, trifluoromethanesulphonic acid, Na₂SO₄, K₂SO₄, ammonium sulphate, H₃PO₄, Na₃PO₄, K₃PO₄, KNO₃, NaNO₃, C₆–C₁₄ arylsulphonic acid such as p-toluenesulphonic acid monohydrate, sulphamic acid, C₁–C₆ alkylsulphonic acid such as methylsulphonic acid and ethylsulphonic acid or acetic acid or mixtures thereof in a concentration of from 0.01M to 15M, 0.01M to 10M or 0.25M to 10M, more typically 1M to 10M, even more typically 1.801M to 10M, 2 to 10M, 2.01M to 10M, 2.5M to 10M, yet even more typically 3 to 10M, yet even more typically 4 to 7M, and yet even more typically 5 to 9M. It is especially preferred to use H₂SO₄ in a concentration of from 0.25M to 10M, more typically 1M to 10M, even more typically 2 to 10M, yet even more typically 3 to 10M, yet even more typically 4 to 10M, and yet even more typically 5 to 9M.

The processes of the invention are typically performed in the temperature range 10–99° C., 25–99° C., or 25–70° C. more typically 25–60° C., more typically 35–60° C.

During the processes of the invention the electrolyte solution is typically stirred or agitated preferably with a mechanical stirrer or by fluidization of the solid reactants using electrolyte solution flow.

The processes of the invention are typically, but not necessarily, conducted under an inert atmosphere such as nitrogen, argon, helium or neon or mixtures thereof.

The positive and negative electrodes can be any shape desired. It is preferred that the positive and negative electrodes are rectangular-plate shaped although the positive electrode can be an expanded metal sheet to allow for zero gap from the membrane while facilitating escape of O₂ gas.

A carbon slurry positive electrode can be used to depolarise the cell and lower the energy requirements.

The positive and negative electrodes of the electrolyte production cell can be carbon and graphite felt, mat, plate, rod, knit, fibre, and cloth; carbon impregnated teflon; carbon impregnated polyethylene; carbon impregnated polypropylene; carbon impregnated polystyrene; carbon impregnated polyvinylchloride; carbon impregnated polyvinylidenechloride; glassy carbon; non-woven carbon fibre material; cellulose; carbon and graphite felt, mat, plate, rod, knit, fibre, and cloth, carbon impregnated teflon, carbon impregnated polyethylene, carbon impregnated polypropylene, carbon impregnated polystyrene, carbon impregnated polyvinylchloride and carbon impregnated polyvinylidenechloride, impregnated with and/or coated with Au, Pt, Ir, Ru, Os, Re, Rh and/or Ag; platinised Ti; platinised Ru; platinised Ir; platinised Pd; Pt; Pt black; dimensionally stabilized anode (DSA—Ti or Ti alloy core, coated at least partially with titanium dioxide which coating is coated or doped in turn with a noble metal coating selected from the group consisting of Pt, Pd, Os, Rh, Ru, Ir and alloys thereof); Au; Pd; Ir; Ru; Os; Re; Rh; Hg; Ag; Tl; Bi; Pb; In; Cd; Ga; Sb; Zn; Pb/Hg; Pb/Bi; Hg/In; Hg/Cd; or Hg/Ga or other suitable electrodes.

In particular the positive electrode can be selected from the group consisting of DSA; Pb; Pb alloy (Eg Pb—Bi alloy); platinised Ti; platinised Ru; platinised Ir; and V₂O₅ coated on Pb, Ti, Zr, Hf, Ta, W or Nb which are also suitable materials for use as positive charge electrodes in an all-vanadium redox charge cell as has been disclosed in the PCT/AU88/00472, the contents of which are incorporated herein by cross reference. V₂O₅ coated electrodes would be unsuitable negative electrodes as they would dissolve. A DSA electrode performs well as a positive or negative electrode.

Preferably a DSA, Pb, V₂O₅ on Pb or graphite anode is used. It is preferred that a Pb or graphite cathode is used.

The electrochemical cell is typically a cell of the “membrane-type”, that is it employs a membrane rather than a diaphragm to separate a positive compartment from a negative compartment. The membrane employed is typically sheet-like and can transport electrolyte ions whilst at the same time being hydraulically-impermeable in contrast to a diaphragm (typically asbestos) which allows restricted electrolyte transfer between compartments. Thus the ionically conducting separator can be a microporous separator such as Daramic (Trade Mark) or a membrane fabricated from a polymer based on perfluorocarboxylic acids or a proton exchange polymer such as sulphonated polystyrene, sulphonated polyethylene or a substantially fluorinated sulphonic acid polymer such as Nafion (Trade Mark) or membranes of Flemion (Trade Mark) or Selemion (Trade Mark) material as manufactured by Asahi Glass Company.

The electrochemical cell includes monopolar and bipolar type cells. A bipolar cell typically includes a plurality of positive compartments each having a positive electrode therein and a plurality of negative compartments each having a negative electrode therein and wherein each of the compartments are separated by a membrane. A bipolar cell is typically of the flat plate- or filter press-type.

By the processes of the invention HED electrolyte solution having vanadium ions in sufficient concentration in an aqueous electrolyte, above saturated concentrations, or 0.5 to 15M or 3M to 10M, 5M to 10M, and more typically 3M to 8M or 5M to 8M which are suitable for use in a practical all-vanadium battery can be prepared in a single step process. Typically a HED aqueous electrolyte having vanadium ions 1.801M to 15M, 2M to 15M, 2.01M to 15M, 3M to 15M or 5M to 15M or 5M to 10M, more typically 3M to 9M or 5 to 9M, yet even 2M to 7M, 2.01M to 5.5M, 2.01M to 7M, 3M to 7M or 5.75 to 6.75M or 7.5 to 7.5M or 6.5 to 7.5M or 5 to 5.5M or 5.5 to 6.5M or 5.001 to 10M or 5.001 to 5.5M, or 5.001 to 6M or 5.001 to 6.5M or 5.001 to 7M or 5.001 to 8M or 5.001 to 9M, for example, vanadium ions (including V(II), V(III), V(IV), and V(V) ions) may be prepared. It is especially preferred to use H₂SO₄ in a concentration of from 0.25M to 17M, more typically 1M to 10M, even more typically 2 to 9M, yet even more typically 3 to 8M, yet even more typically 4 to 9M, and yet even more typically 5 to 9M. By passage of the appropriate number of coulombs an electrolyte solution consisting of 50% M V(III) to 50% M V(IV) can be obtained. Equal volumes of this solution can then be used for each ½-cell so that no overcharge of the positive side is required for the initial charging process.

If precipitation of any of the vanadium ions does eventually occur however, it can easily be redissolved by combining the catholyte with the anolyte. This will result in dissolution of the precipitate forming a solution which is mixture of V(III) and V(IV) as in an uncharged battery which can readily be recharged and return the battery to its original state. Occasional mixing of the catholyte and anolyte is beneficial as it assists in rebalancing the cell. Unequal rates of diffusion of the different ions of vanadium across a membrane gradually leads to a greater concentration of vanadium ions on one side, but by periodically mixing the catholyte and anolyte and equally dividing the volumes into the +ve and −ve tanks, a rebalanced cell can be readily achieved. Alternatively any precipitate formed in the battery can be redissolved by reversing the polarity of the cell or stack (or battery) and slowly recharging the electrolyte solutions.

A further embodiment of the invention involves an electrochemical apparatus for power delivery employing an array of cells comprising a positive electrode at one end of the array, a negative electrode at the other end of the array, and one or more bipolar electrodes between the end electrodes. A hydrogen peroxide solution or a bubbly dispersion of air/oxygen in an electrolyte solution is pumped through the positive ½-cells of the array while a HED solution of V(II) or V(II)/V(III) is pumped through the negative ½-cells to produce energy (and thus electricity) according to the reactions:

Positive electrode: ½O₂+2H⁺+2e→H₂O

Negative electrode: 2V²⁺→2V³⁺+2e

Typically the electrolyte solution is circulated separately through the the positive and negative compartments

The vanadium ions may be in a concentration of up to and including a supersaturated concentration.

Stabilised Electrolyte Solution

According to a further embodiment of the present invention there is provided a stabilised electrolyte solution for use in a redox cell, the stabilised electrolyte solution comprising redox ions, an electrolyte and a stabilising amount of a stabilising agent.

The redox ions may be metal ions including transition metal ions (including the various forms of metal ions that exist in the solution under consideration) and the redox couple may be a metal ion redox couple (including the various forms of couples that exist in the solution under consideration). Examples of redox ions are vanadium ions, chromium ions, tin ions, titanium ions, iron ions, manganese ions, molybdenum ions, lead ions, nickel ions, copper ions, cobalt ions, cerium ions, bismuth ions, silver ions, gold ions, cadmium ions, mercury ions, platinum ions, palladium ions, iridium ions, osmium ions, rhenium ions, tungsten ions, tantalum ions, zirconium ions, hafnium ions, lanthanum ions, europium ions, samarium ions, neodymium ions, yttrium ions, zirconium ions, and niobium ions or any mixture thereof, for example (eg in a concentration range up to and including a supersaturated concentration, such as above 1.8M, above 2M, 0.25M to 10M, 2M to 10M, 2M to 9M, 2M to 8M, 2.5M to 9M, 2.8M to 8M, 3M to 7M, 3M to 6M, 4M to 6.5M, 5.001M to 10M, 5.001M to 7.5M, 5.001M to 10M, 5.001M to 7.0M, and 5.001M to 6M). Vanadium redox ions and vanadium redox couples are especially suitable to use in the invention (especially in a concentration range such as above 1.8M, above 2M, 0.25M to 10M, 2M to 10M, 2M to 9M, 2M to 8M, 2.5M to 9M, 2.8M to 8M, 3M to 7M, 3M to 6M, 4M to 6.5M, 5.001M to 10M, 5.001M to 7.5M, 5.001M to 10M, 5.001M to 7.0M, and 5.001M to 6M). A stabilised electrolyte solution wherein the redox ions are selected from the group consisting of pentavalent vanadium ions, tetravalent vanadium ions, trivalent vanadium ions, divalent vanadium ions, a mixture of divalent and trivalent vanadium ions, a mixture of divalent and tetravalent vanadium ions, a mixture of trivalent and tetravalent vanadium ions, a mixture of divalent, trivalent and tetravalent vanadium ions, a mixture of divalent, trivalent, tetravalent and pentavalent vanadium ions, a mixture of tetravalent and pentavalent vanadium ions is particularly useful.

According to another embodiment of the present invention there is provided a stabilised electrolyte solution for use in a redox cell comprising an aqueous solution of redox ions, an electrolyte and a stabilising amount of a stabilising agent.

According to a further embodiment of the present invention there is provided a redox cell or redox battery comprising a stabilised electrolyte solution produced by the method of the invention.

Typically the redox cell is an all vanadium redox cell and the redox battery is an all vanadium redox battery.

According to a further embodiment of this invention there is provided a redox battery having a positive compartment containing a catholyte in electrical contact with a positive electrode, the catholyte comprising an electrolyte solution containing redox ions selected from the group consisting of a catholyte redox couple, catholyte redox ions and a mixture of an catholyte redox couple and catholyte redox ions, a negative compartment containing an anolyte in electrical contact with a negative electrode, the anolyte comprising an electrolyte solution containing redox ions selected from the group consisting of an anolyte redox couple, anolyte redox ions and a mixture of an anolyte redox couple and anolyte redox ions, and a separator or membrane disposed between the positive and negative compartments and in contact with the catholyte and anolyte to provide ionic communication therebetween, at least one of the electrolyte solutions having an effective stabilising amount of a stabilising agent for stabilising the redox ions in at least one of the electrolyte solutions.

The redox ions may be stabilised at up to and including a supersaturated concentration.

In the HED vanadium redox battery, conditions that may be maintained and/or controlled apart from electrolyte concentration in the anolyte and/or catholyte (e.g. sulphuric acid concentration and/or total sulphate concentration) and/or temperature of the anolyte and/or catholyte solutions, include pH's of the anolyte and/or catholyte, pumping rates of the anolyte and/or catholyte through the negative and positive compartments, concentrations of the stabilizing agent(s) in the anolyte and/or catholyte, concentrations of the various vanadium redox ions and/or couples in the anolyte and/or catholyte, and oxygen concentrations of the various vanadium redox ions and/or couples in the anolyte and/or catholyte. The pH and concentrations and pumping rates of the above mentioned species may be measured by appropriate probes or other means known in the art.

An all-vanadium redox battery system is also provided consisting of a combination of the all-vanadium redox battery of the invention and an anolyte reservoir for storing anolyte coupled to the negative compartment by anolyte supply and return lines via a pump and a catholyte reservoir for storing catholyte coupled to the positive compartment by catholyte supply and return lines via a pump.

In the HED vanadium redox cell, typically, the solution is an aqueous solution and the vanadium redox ions (and electrolyte e.g. sulphuric acid optionally expressed as total sulphate concentration) are (each) present in a range selected from the group consisting of 1.801M, optionally 2M up to and including a highly supersaturated concentration, aM, bM, a concentration in the range aM–bM, and a concentration range in the range aM–bM, where a is selected from the group consisting of a value presented in the column headed “a” in Table A* below at one of entries 1–26, and b is selected from the group of the values presented in the column headed “b” adjacent the corresponding “a” entry:

TABLE A* Entry a b 1 0.1 1, 1.25, 1.5, 1.75, 2, 2.25, 2.5, 2.75, 3, 3.25, 3.5, 3.75, 4, 4.25, 4.5, 4.75, 5, 5.25, 5.5, 5.75, 6, 6.25, 6.5, 6.75, 7, 7.25, 7.5, 7.75, 8, 8.25, 8.5, 8.75, 9, 9.25, 9.5, 9.75, 10, 10.25, 10.5, 10.75, 11, 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5 2 0.25 1, 1.25, 1.5, 1.75, 2, 2.25, 2.5, 2.75, 3, 3.25, 3.5, 3.75, 4, 4.25, 4.5, 4.75, 5, 5.25, 5.5, 5.75, 6, 6.25, 6.5, 6.75, 7, 7.25, 7.5, 7.75, 8, 8.25, 8.5, 8.75, 9, 9.25, 9.5, 9.75, 10, 10.25, 10.5, 10.75, 11, 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5 3 0.5 1, 1.25, 1.5, 1.75, 2, 2.25, 2.5, 2.75, 3, 3.25, 3.5, 3.75, 4, 4.25, 4.5, 4.75, 5, 5.25, 5.5, 5.75, 6, 6.25, 6.5, 6.75, 7, 7.25, 7.5, 7.75, 8, 8.25, 8.5, 8.75, 9, 9.25, 9.5, 9.75, 10, 10.25, 10.5, 10.75, 11, 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5 4 0.75 1, 1.25, 1.5, 1.75, 2, 2.25, 2.5, 2.75, 3, 3.25, 3.5, 3.75, 4, 4.25, 4.5, 4.75, 5, 5.25, 5.5, 5.75, 6, 6.25, 6.5, 6.75, 7, 7.25, 7.5, 7.75, 8, 8.25, 8.5, 8.75, 9, 9.25, 9.5, 9.75, 10, 10.25, 10.5, 10.75, 11, 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5 5 1 1.25, 1.5, 1.75, 2, 2.25, 2.5, 2.75, 3, 3.25, 3.5, 3.75, 4, 4.25, 4.5, 4.75, 5, 5.25, 5.5, 5.75, 6, 6.25, 6.5, 6.75, 7, 7.25, 7.5, 7.75, 8, 8.25, 8.5, 8.75, 9, 9.25, 9.5, 9.75, 10, 10.25, 10.5, 10.75, 11, 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5 6 1.25 1.5, 1.75, 2, 2.25, 2.5, 2.75, 3, 3.25, 3.5, 3.75, 4, 4.25, 4.5, 4.75, 5, 5.25, 5.5, 5.75, 6, 6.25, 6.5, 6.75, 7, 7.25, 7.5, 7.75, 8, 8.25, 8.5, 8.75, 9, 9.25, 9.5, 9.75, 10, 10.25, 10.5, 10.75, 11, 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5 7 1.5 1.75, 2, 2.25, 2.5, 2.75, 3, 3.25, 3.5, 3.75, 4, 4.25, 4.5, 4.75, 5, 5.25, 5.5, 5.75, 6, 6.25, 6.5, 6.75, 7, 7.25, 7.5, 7.75, 8, 8.25, 8.5, 8.75, 9, 9.25, 9.5, 9.75, 10, 10.25, 10.5, 10.75, 11, 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5 8 1.75 2, 2.25, 2.5, 2.75, 3, 3.25, 3.5, 3.75, 4, 4.25, 4.5, 4.75, 5, 5.25, 5.5, 5.75, 6, 6.25, 6.5, 6.75, 7, 7.25, 7.5, 7.75, 8, 8.25, 8.5, 8.75, 9, 9.25, 9.5, 9.75, 10, 10.25, 10.5, 10.75, 11, 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5 9 2 2.25, 2.5, 2.75, 3, 3.25, 3.5, 3.75, 4, 4.25, 4.5, 4.75, 5, 5.25, 5.5, 5.75, 6, 6.25, 6.5, 6.75, 7, 7.25, 7.5, 7.75, 8, 8.25, 8.5, 8.75, 9, 9.25, 9.5, 9.75, 10, 10.25, 10.5, 10.75, 11, 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5 10 2.25 2.5, 2.75, 3, 3.25, 3.5, 3.75, 4, 4.25, 4.5, 4.75, 5, 5.25, 5.5, 5.75, 6, 6.25, 6.5, 6.75, 7, 7.25, 7.5, 7.75, 8, 8.25, 8.5, 8.75, 9, 9.25, 9.5, 9.75, 10, 10.25, 10.5, 10.75, 11, 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5 11 2.5 2.75, 3, 3.25, 3.5, 3.75, 4, 4.25, 4.5, 4.75, 5, 5.25, 5.5, 5.75, 6, 6.25, 6.5, 6.75, 7, 7.25, 7.5, 7.75, 8, 8.25, 8.5, 8.75, 9, 9.25, 9.5, 9.75, 10, 10.25, 10.5, 10.75, 11, 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5 12 2.75 3, 3.25, 3.5, 3.75, 4, 4.25, 4.5, 4.75, 5, 5.25, 5.5, 5.75, 6, 6.25, 6.5, 6.75, 7, 7.25, 7.5, 7.75, 8, 8.25, 8.5, 8.75, 9, 9.25, 9.5, 9.75, 10, 10.25, 10.5, 10.75, 11, 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5 13 3 3.25, 3.5, 3.75, 4, 4.25, 4.5, 4.75, 5, 5.25, 5.5, 5.75, 6, 6.25, 6.5, 6.75, 7, 7.25, 7.5, 7.75, 8, 8.25, 8.5, 8.75, 9, 9.25, 9.5, 9.75, 10, 10.25, 10.5, 10.75, 11, 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5 14 3.25 3.5, 3.75, 4, 4.25, 4.5, 4.75, 5, 5.25, 5.5, 5.75, 6, 6.25, 6.5, 6.75, 7, 7.25, 7.5, 7.75, 8, 8.25, 8.5, 8.75, 9, 9.25, 9.5, 9.75, 10, 10.25, 10.5, 10.75, 11, 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5 15 3.5 3.75, 4, 4.25, 4.5, 4.75, 5, 5.25, 5.5, 5.75, 6, 6.25, 6.5, 6.75, 7, 7.25, 7.5, 7.75, 8, 8.25, 8.5, 8.75, 9, 9.25, 9.5, 9.75, 10, 10.25, 10.5, 10.75, 11, 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5 16 3.75 4, 4.25, 4.5, 4.75, 5, 5.25, 5.5, 5.75, 6, 6.25, 6.5, 6.75, 7, 7.25, 7.5, 7.75, 8, 8.25, 8.5, 8.75, 9, 9.25, 9.5, 9.75, 10, 10.25, 10.5, 10.75, 11, 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5 17 4 4.25, 4.5, 4.75, 5, 5.25, 5.5, 5.75, 6, 6.25, 6.5, 6.75, 7, 7.25, 7.5, 7.75, 8, 8.25, 8.5, 8.75, 9, 9.25, 9.5, 9.75, 10, 10.25, 10.5, 10.75, 11, 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5 18 4.25 4.5, 4.75, 5, 5.25, 5.5, 5.75, 6, 6.25, 6.5, 6.75, 7, 7.25, 7.5, 7.75, 8, 8.25, 8.5, 8.75, 9, 9.25, 9.5, 9.75, 10, 10.25, 10.5, 10.75, 11, 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5 19 4.5 4.75, 5, 5.25, 5.5, 5.75, 6, 6.25, 6.5, 6.75, 7, 7.25, 7.5, 7.75, 8, 8.25, 8.5, 8.75, 9, 9.25, 9.5, 9.75, 10, 10.25, 10.5, 10.75, 11, 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5 20 4.75 5, 5.25, 5.5, 5.75, 6, 6.25, 6.5, 6.75, 7, 7.25, 7.5, 7.75, 8, 8.25, 8.5, 8.75, 9, 9.25, 9.5, 9.75, 10, 10.25, 10.5, 10.75, 11, 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5 21 5 5.25, 5.5, 5.75, 6, 6.25, 6.5, 6.75, 7, 7.25, 7.5, 7.75, 8, 8.25, 8.5, 8.75, 9, 9.25, 9.5, 9.75, 10, 10.25, 10.5, 10.75, 11, 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5 22 6 6.25, 6.5, 6.75, 7, 7.25, 7.5, 7.75, 8, 8.25, 8.5, 8.75, 9, 9.25, 9.5, 9.75, 10, 10.25, 10.5, 10.75, 11, 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5 23 7 7.25, 7.5, 7.75, 8, 8.25, 8.5, 8.75, 9, 9.25, 9.5, 9.75, 10, 10.25, 10.5, 10.75, 11, 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5 24 8 8.25, 8.5, 8.75, 9, 9.25, 9.5, 9.75, 10, 10.25, 10.5, 10.75, 11, 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5 25 9 9.25, 9.5, 9.75, 10, 10.25, 10.5, 10.75, 11, 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5 26 10 10.25, 10.5, 10.75, 11, 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5

Advantageously where a sulphate electrolyte is used (e.g. sulphuric acid) the mole:mole ratio of vanadium ions:total sulphate is from 0.1 to 1, typically 2:5. Thus for a 2M vanadium ion solution 5M total sulphate is typically used. For 1.801–5M vanadium ion concentration 5–7M total sulphate is typically used as the electrolyte concentration.

Advantageously the stabilised electrolyte solution is selected from the group consisting of a stabilised electrolyte anolyte solution and a stabilised electrolyte catholyte solution.

Generally the redox ions are selected from the group consisting of pentavalent vanadium ions, tetravalent vanadium ions, trivalent vanadium ions, divalent vanadium ions, a mixture of divalent and trivalent vanadium ions, a mixture of divalent and tetravalent vanadium ions, a mixture of trivalent and tetravalent vanadium ions, a mixture of divalent, trivalent and tetravalent vanadium ions, a mixture of divalent, trivalent, tetravalent and pentavalent vanadium ions, a mixture of trivalent, tetravalent and pentavalent vanadium ions and a mixture of tetravalent and pentavalent vanadium ions.

Advantageously the stabilising agent is present in a range selected from the group consisting of c % wt/vol of the solution, c % wt/wt of the solution, c % wt/wt of the vanadium ions in the solution, c % vol/vol of the solution, c % vol/wt of the solution, c % vol/wt of the vanadium ions in the solution, c % mole/mole, d % wt/vol of the solution, d % wt/wt of the solution, d % wt/wt of the vanadium ions in the solution, d % vol/vol of the solution, d % vol/wt of the solution, d % vol/wt of the vanadium ions in the solution, d % mole/mole, c % to d % wt/vol of the solution, c % to d % wt/wt of the solution, c % to d % wt/wt of the vanadium ions in the solution, c % to d % vol/vol of the solution, c % to d % vol/wt of the solution, c % to d % vol/wt of the vanadium ions in the solution, and c % to d % mole/mole of the vanadium ions in the solution, where c is selected from the group consisting of a value presented in the column headed “c” in Table B* below at one of entries 1–33, and d is selected from the group of the values presented in the column headed “d” adjacent the corresponding “c” entry.

TABLE B* Entry c d 1 0.01 0.025, 0.05, 0.075, 0.1, 0.25, 0.5, 0.75, 1, 1.25, 1.5, 1.75, 2, 2.25, 2.5, 2.75, 3, 3.25, 3.5, 3.75, 4, 4.25, 4.5, 4.75, 5, 5.25, 5.5, 5.75, 6, 6.25, 6.5, 6.75, 7, 7.25, 7.5, 7.75, 8, 8.25, 8.5, 8.75, 9, 9.25, 9.5, 9.75, 10, 10.25, 10.5, 10.75, 11, 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5, 19, 19.5, 20, 25, 30 2 0.025 0.05, 0.075, 0.1, 0.25, 0.5, 0.75, 1, 1.25, 1.5, 1.75, 2, 2.25, 2.5, 2.75, 3, 3.25, 3.5, 3.75, 4, 4.25, 4.5, 4.75, 5, 5.25, 5.5, 5.75, 6, 6.25, 6.5, 6.75, 7, 7.25, 7.5, 7.75, 8, 8.25, 8.5, 8.75, 9, 9.25, 9.5, 9.75, 10, 10.25, 10.5, 10.75, 11, 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5, 19, 19.5, 20, 25, 30 3 0.05 0.075, 0.1, 0.25, 0.5, 0.75, 1, 1.25, 1.5, 1.75, 2, 2.25, 2.5, 2.75, 3, 3.25, 3.5, 3.75, 4, 4.25, 4.5, 4.75, 5, 5.25, 5.5, 5.75, 6, 6.25, 6.5, 6.75, 7, 7.25, 7.5, 7.75, 8, 8.25, 8.5, 8.75, 9, 9.25, 9.5, 9.75, 10, 10.25, 10.5, 10.75, 11, 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5, 19, 19.5, 20, 25, 30 4 0.075 0.1, 0.25, 0.5, 0.75, 1, 1.25, 1.5, 1.75, 2, 2.25, 2.5, 2.75, 3, 3.25, 3.5, 3.75, 4, 4.25, 4.5, 4.75, 5, 5.25, 5.5, 5.75, 6, 6.25, 6.5, 6.75, 7, 7.25, 7.5, 7.75, 8, 8.25, 8.5, 8.75, 9, 9.25, 9.5, 9.75, 10, 10.25, 10.5, 10.75, 11, 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5, 19, 19.5, 20, 25, 30 5 0.1 0.25, 0.5, 0.75, 1, 1.25, 1.5, 1.75, 2, 2.25, 2.5, 2.75, 3, 3.25, 3.5, 3.75, 4, 4.25, 4.5, 4.75, 5, 5.25, 5.5, 5.75, 6, 6.25, 6.5, 6.75, 7, 7.25, 7.5, 7.75, 8, 8.25, 8.5, 8.75, 9, 9.25, 9.5, 9.75, 10, 10.25, 10.5, 10.75, 11, 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5, 19, 19.5, 20, 25, 30 6 0.25 0.5, 0.75, 1, 1.25, 1.5, 1.75, 2, 2.25, 2.5, 2.75, 3, 3.25, 3.5, 3.75, 4, 4.25, 4.5, 4.75, 5, 5.25, 5.5, 5.75, 6, 6.25, 6.5, 6.75, 7, 7.25, 7.5, 7.75, 8, 8.25, 8.5, 8.75, 9, 9.25, 9.5, 9.75, 10, 10.25, 10.5, 10.75, 11, 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5, 19, 19.5, 20, 25, 30 7 0.5 0.75, 1, 1.25, 1.5, 1.75, 2, 2.25, 2.5, 2.75, 3, 3.25, 3.5, 3.75, 4, 4.25, 4.5, 4.75, 5, 5.25, 5.5, 5.75, 6, 6.25, 6.5, 6.75, 7, 7.25, 7.5, 7.75, 8, 8.25, 8.5, 8.75, 9, 9.25, 9.5, 9.75, 10, 10.25, 10.5, 10.75, 11, 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5, 19, 19.5, 20, 25, 30 8 0.75 1, 1.25, 1.5, 1.75, 2, 2.25, 2.5, 2.75, 3, 3.25, 3.5, 3.75, 4, 4.25, 4.5, 4.75, 5, 5.25, 5.5, 5.75, 6, 6.25, 6.5, 6.75, 7, 7.25, 7.5, 7.75, 8, 8.25, 8.5, 8.75, 9, 9.25, 9.5, 9.75, 10, 10.25, 10.5, 10.75, 11, 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5, 19, 19.5, 20, 25, 30 9 1 1.25, 1.5, 1.75, 2, 2.25, 2.5, 2.75, 3, 3.25, 3.5, 3.75, 4, 4.25, 4.5, 4.75, 5, 5.25, 5.5, 5.75, 6, 6.25, 6.5, 6.75, 7, 7.25, 7.5, 7.75, 8, 8.25, 8.5, 8.75, 9, 9.25, 9.5, 9.75, 10, 10.25, 10.5, 10.75, 11, 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5, 19, 19.5, 20, 25, 30 10 1.25 1.5, 1.75, 2, 2.25, 2.5, 2.75, 3, 3.25, 3.5, 3.75, 4, 4.25, 4.5, 4.75, 5, 5.25, 5.5, 5.75, 6, 6.25, 6.5, 6.75, 7, 7.25, 7.5, 7.75, 8, 8.25, 8.5, 8.75, 9, 9.25, 9.5, 9.75, 10, 10.25, 10.5, 10.75, 11, 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5, 19, 19.5, 20, 25, 30 11 1.5 1.75, 2, 2.25, 2.5, 2.75, 3, 3.25, 3.5, 3.75, 4, 4.25, 4.5, 4.75, 5, 5.25, 5.5, 5.75, 6, 6.25, 6.5, 6.75, 7, 7.25, 7.5, 7.75, 8, 8.25, 8.5, 8.75, 9, 9.25, 9.5, 9.75, 10, 10.25, 10.5, 10.75, 11, 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5, 19, 19.5, 20, 25, 30 12 1.75 2, 2.25, 2.5, 2.75, 3, 3.25, 3.5, 3.75, 4, 4.25, 4.5, 4.75, 5, 5.25, 5.5, 5.75, 6, 6.25, 6.5, 6.75, 7, 7.25, 7.5, 7.75, 8, 8.25, 8.5, 8.75, 9, 9.25, 9.5, 9.75, 10, 10.25, 10.5, 10.75, 11, 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5, 19, 19.5, 20, 25, 30 13 2 2.25, 2.5, 2.75, 3, 3.25, 3.5, 3.75, 4, 4.25, 4.5, 4.75, 5, 5.25, 5.5, 5.75, 6, 6.25, 6.5, 6.75, 7, 7.25, 7.5, 7.75, 8, 8.25, 8.5, 8.75, 9, 9.25, 9.5, 9.75, 10, 10.25, 10.5, 10.75, 11, 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5, 19, 19.5, 20, 25, 30 14 2.25 2.5, 2.75, 3, 3.25, 3.5, 3.75, 4, 4.25, 4.5, 4.75, 5, 5.25, 5.5, 5.75, 6, 6.25, 6.5, 6.75, 7, 7.25, 7.5, 7.75, 8, 8.25, 8.5, 8.75, 9, 9.25, 9.5, 9.75, 10, 10.25, 10.5, 10.75, 11, 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5, 19, 19.5, 20, 25, 30 15 2.5 2.75, 3, 3.25, 3.5, 3.75, 4, 4.25, 4.5, 4.75, 5, 5.25, 5.5, 5.75, 6, 6.25, 6.5, 6.75, 7, 7.25, 7.5, 7.75, 8, 8.25, 8.5, 8.75, 9, 9.25, 9.5, 9.75, 10, 10.25, 10.5, 10.75, 11, 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5, 19, 19.5, 20, 25, 30 16 2.75 3, 3.25, 3.5, 3.75, 4, 4.25, 4.5, 4.75, 5, 5.25, 5.5, 5.75, 6, 6.25, 6.5, 6.75, 7, 7.25, 7.5, 7.75, 8, 8.25, 8.5, 8.75, 9, 9.25, 9.5, 9.75, 10, 10.25, 10.5, 10.75, 11, 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5, 19, 19.5, 20, 25, 30 17 3 3.25, 3.5, 3.75, 4, 4.25, 4.5, 4.75, 5, 5.25, 5.5, 5.75, 6, 6.25, 6.5, 6.75, 7, 7.25, 7.5, 7.75, 8, 8.25, 8.5, 8.75, 9, 9.25, 9.5, 9.75, 10, 10.25, 10.5, 10.75, 11, 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5, 19, 19.5, 20, 25, 30 18 3.25 3.5, 3.75, 4, 4.25, 4.5, 4.75, 5, 5.25, 5.5, 5.75, 6, 6.25, 6.5, 6.75, 7, 7.25, 7.5, 7.75, 8, 8.25, 8.5, 8.75, 9, 9.25, 9.5, 9.75, 10, 10.25, 10.5, 10.75, 11, 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5, 19, 19.5, 20, 25, 30 19 3.5 3.75, 4, 4.25, 4.5, 4.75, 5, 5.25, 5.5, 5.75, 6, 6.25, 6.5, 6.75, 7, 7.25, 7.5, 7.75, 8, 8.25, 8.5, 8.75, 9, 9.25, 9.5, 9.75, 10, 10.25, 10.5, 10.75, 11, 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5, 19, 19.5, 20, 25, 30 20 3.75 4, 4.25, 4.5, 4.75, 5, 5.25, 5.5, 5.75, 6, 6.25, 6.5, 6.75, 7, 7.25, 7.5, 7.75, 8, 8.25, 8.5, 8.75, 9, 9.25, 9.5, 9.75, 10, 10.25, 10.5, 10.75, 11, 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5, 19, 19.5, 20, 25, 30 21 4 4.25, 4.5, 4.75, 5, 5.25, 5.5, 5.75, 6, 6.25, 6.5, 6.75, 7, 7.25, 7.5, 7.75, 8, 8.25, 8.5, 8.75, 9, 9.25, 9.5, 9.75, 10, 10.25, 10.5, 10.75, 11, 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5, 19, 19.5, 20, 25, 30 22 4.5 4.75, 5, 5.25, 5.5, 5.75, 6, 6.25, 6.5, 6.75, 7, 7.25, 7.5, 7.75, 8, 8.25, 8.5, 8.75, 9, 9.25, 9.5, 9.75, 10, 10.25, 10.5, 10.75, 11, 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5, 19, 19.5, 20, 25, 30 23 5 5.25, 5.5, 5.75, 6, 6.25, 6.5, 6.75, 7, 7.25, 7.5, 7.75, 8, 8.25, 8.5, 8.75, 9, 9.25, 9.5, 9.75, 10, 10.25, 10.5, 10.75, 11, 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5, 19, 19.5, 20, 25, 30 24 6 6.25, 6.5, 6.75, 7, 7.25, 7.5, 7.75, 8, 8.25, 8.5, 8.75, 9, 9.25, 9.5, 9.75, 10, 10.25, 10.5, 10.75, 11, 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5, 19, 19.5, 20, 25, 30 25 7 7.25, 7.5, 7.75, 8, 8.25, 8.5, 8.75, 9, 9.25, 9.5, 9.75, 10, 10.25, 10.5, 10.75, 11, 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5, 19, 19.5, 20, 25, 30 26 8 8.25, 8.5, 8.75, 9, 9.25, 9.5, 9.75, 10, 10.25, 10.5, 10.75, 11, 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5, 19, 19.5, 20, 25, 30 27 9 9.25, 9.5, 9.75, 10, 10.25, 10.5, 10.75, 11, 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5, 19, 19.5, 20, 25, 30 28 10 10.25, 10.5, 10.75, 11, 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5, 19, 19.5, 20, 25, 30 29 11 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5, 19, 19.5, 20, 25, 30 30 12 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5, 19, 19.5, 20, 25, 30 31 13 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5, 19, 19.5, 20, 25, 30 32 14 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5, 19, 19.5, 20, 25, 30 33 15 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5, 19, 19.5, 20, 25, 30

Advantageously the solution is stabilised at a temperature selected from the group consisting of e° C., f° C., a temperature range e° C.–f° C. and a temperature range in the range e° C.–f° C. where e is selected from the group consisting of a value presented in the column headed “e” in Table C* below at one of entries 1–14, and f is selected from the group of the values presented in the column headed “f” adjacent the corresponding “e” entry.

TABLE C* Entry e f 1 0 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 80, 90 2 5 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 80, 90 3 10 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 80, 90 4 15 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 80, 90 5 20 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 80, 90 6 25 30, 35, 40, 45, 50, 55, 60, 65, 70, 80, 90 7 30 35, 40, 45, 50, 55, 60, 65, 70, 80, 90 8 35 40, 45, 50, 55, 60, 65, 70, 80, 90 9 40 45, 50, 55, 60, 65, 70, 80, 90 10 45 50, 55, 60, 65, 70, 80, 90 11 50 55, 60, 65, 70, 80, 90 12 55 60, 65, 70, 80, 90 13 60 65, 70, 80, 90 14 65 70, 80, 90

Typically at least one period is for a period in the range g months-h months where g is selected from the group consisting of a value presented in the column headed “g” in Table D below at one of entries 1–33, and h is selected from the group of the values presented in the column headed “h” adjacent the corresponding “g” entry.

TABLE D Entry g h 1 0.01 0.025, 0.05, 0.075, 0.1, 0.25, 0.5, 0.75, 1, 1.25, 1.5, 1.75, 2, 2.25, 2.5, 2.75, 3, 3.25, 3.5, 3.75, 4, 4.25, 4.5, 4.75, 5, 5.25, 5.5, 5.75, 6, 6.25, 6.5, 6.75, 7, 7.25, 7.5, 7.75, 8, 8.25, 8.5, 8.75, 9, 9.25, 9.5, 9.75, 10, 10.25, 10.5, 10.75, 11, 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5, 19, 19.5, 20, 25, 30, 40, 50, 60, 70, 100, 150, 200, 250, 300, 350, 400, 500, 600, 700, 1000 2 0.025 0.05, 0.075, 0.1, 0.25, 0.5, 0.75, 1, 1.25, 1.5, 1.75, 2, 2.25, 2.5, 2.75, 3, 3.25, 3.5, 3.75, 4, 4.25, 4.5, 4.75, 5, 5.25, 5.5, 5.75, 6, 6.25, 6.5, 6.75, 7, 7.25, 7.5, 7.75, 8, 8.25, 8.5, 8.75, 9, 9.25, 9.5, 9.75, 10, 10.25, 10.5, 10.75, 11, 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5, 19, 19.5, 20, 25, 30, 40, 50, 60, 70, 100, 150, 200, 250, 300, 350, 400, 500, 600, 700, 1000 3 0.05 0.075, 0.1, 0.25, 0.5, 0.75, 1, 1.25, 1.5, 1.75, 2, 2.25, 2.5, 2.75, 3, 3.25, 3.5, 3.75, 4, 4.25, 4.5, 4.75, 5, 5.25, 5.5, 5.75, 6, 6.25, 6.5, 6.75, 7, 7.25, 7.5, 7.75, 8, 8.25, 8.5, 8.75, 9, 9.25, 9.5, 9.75, 10, 10.25, 10.5, 10.75, 11, 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5, 19, 19.5, 20, 25, 30, 40, 50, 60, 70, 100, 150, 200, 250, 300, 350, 400, 500, 600, 700, 1000 4 0.075 0.1, 0.25, 0.5, 0.75, 1, 1.25, 1.5, 1.75, 2, 2.25, 2.5, 2.75, 3, 3.25, 3.5, 3.75, 4, 4.25, 4.5, 4.75, 5, 5.25, 5.5, 5.75, 6, 6.25, 6.5, 6.75, 7, 7.25, 7.5, 7.75, 8, 8.25, 8.5, 8.75, 9, 9.25, 9.5, 9.75, 10, 10.25, 10.5, 10.75, 11, 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5, 19, 19.5, 20, 25, 30, 40, 50, 60, 70, 100, 150, 200, 250, 300, 350, 400, 500, 600, 700, 1000 5 0.1 0.25, 0.5, 0.75, 1, 1.25, 1.5, 1.75, 2, 2.25, 2.5, 2.75, 3, 3.25, 3.5, 3.75, 4, 4.25, 4.5, 4.75, 5, 5.25, 5.5, 5.75, 6, 6.25, 6.5, 6.75, 7, 7.25, 7.5, 7.75, 8, 8.25, 8.5, 8.75, 9, 9.25, 9.5, 9.75, 10, 10.25, 10.5, 10.75, 11, 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5, 19, 19.5, 20, 25, 30, 40, 50, 60, 70, 100, 150, 200, 250, 300, 350, 400, 500, 600, 700, 1000 6 0.25 0.5, 0.75, 1, 1.25, 1.5, 1.75, 2, 2.25, 2.5, 2.75, 3, 3.25, 3.5, 3.75, 4, 4.25, 4.5, 4.75, 5, 5.25, 5.5, 5.75, 6, 6.25, 6.5, 6.75, 7, 7.25, 7.5, 7.75, 8, 8.25, 8.5, 8.75, 9, 9.25, 9.5, 9.75, 10, 10.25, 10.5, 10.75, 11, 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5, 19, 19.5, 20, 25, 30, 40, 50, 60, 70, 100, 150, 200, 250, 300, 350, 400, 500, 600, 700, 1000 7 0.5 0.75, 1, 1.25, 1.5, 1.75, 2, 2.25, 2.5, 2.75, 3, 3.25, 3.5, 3.75, 4, 4.25, 4.5, 4.75, 5, 5.25, 5.5, 5.75, 6, 6.25, 6.5, 6.75, 7, 7.25, 7.5, 7.75, 8, 8.25, 8.5, 8.75, 9, 9.25, 9.5, 9.75, 10, 10.25, 10.5, 10.75, 11, 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5, 19, 19.5, 20, 25, 30, 40, 50, 60, 70, 100, 150, 200, 250, 300, 350, 400, 500, 600, 700, 1000 8 0.75 1, 1.25, 1.5, 1.75, 2, 2.25, 2.5, 2.75, 3, 3.25, 3.5, 3.75, 4, 4.25, 4.5, 4.75, 5, 5.25, 5.5, 5.75, 6, 6.25, 6.5, 6.75, 7, 7.25, 7.5, 7.75, 8, 8.25, 8.5, 8.75, 9, 9.25, 9.5, 9.75, 10, 10.25, 10.5, 10.75, 11, 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5, 19, 19.5, 20, 25, 30, 40, 50, 60, 70, 100, 150, 200, 250, 300, 350, 400, 500, 600, 700, 1000 9 1 1.25, 1.5, 1.75, 2, 2.25, 2.5, 2.75, 3, 3.25, 3.5, 3.75, 4, 4.25, 4.5, 4.75, 5, 5.25, 5.5, 5.75, 6, 6.25, 6.5, 6.75, 7, 7.25, 7.5, 7.75, 8, 8.25, 8.5, 8.75, 9, 9.25, 9.5, 9.75, 10, 10.25, 10.5, 10.75, 11, 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5, 19, 19.5, 20, 25, 30, 40, 50, 60, 70, 100, 150, 200, 250, 300, 350, 400, 500, 600, 700, 1000 10 1.25 1.5, 1.75, 2, 2.25, 2.5, 2.75, 3, 3.25, 3.5, 3.75, 4, 4.25, 4.5, 4.75, 5, 5.25, 5.5, 5.75, 6, 6.25, 6.5, 6.75, 7, 7.25, 7.5, 7.75, 8, 8.25, 8.5, 8.75, 9, 9.25, 9.5, 9.75, 10, 10.25, 10.5, 10.75, 11, 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5, 19, 19.5, 20, 25, 30, 40, 50, 60, 70, 100, 150, 200, 250, 300, 350, 400, 500, 600, 700, 1000 11 1.5 1.75, 2, 2.25, 2.5, 2.75, 3, 3.25, 3.5, 3.75, 4, 4.25, 4.5, 4.75, 5, 5.25, 5.5, 5.75, 6, 6.25, 6.5, 6.75, 7, 7.25, 7.5, 7.75, 8, 8.25, 8.5, 8.75, 9, 9.25, 9.5, 9.75, 10, 10.25, 10.5, 10.75, 11, 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5, 19, 19.5, 20, 25, 30, 40, 50, 60, 70, 100, 150, 200, 250, 300, 350, 400, 500, 600, 700, 1000 12 1.75 2, 2.25, 2.5, 2.75, 3, 3.25, 3.5, 3.75, 4, 4.25, 4.5, 4.75, 5, 5.25, 5.5, 5.75, 6, 6.25, 6.5, 6.75, 7, 7.25, 7.5, 7.75, 8, 8.25, 8.5, 8.75, 9, 9.25, 9.5, 9.75, 10, 10.25, 10.5, 10.75, 11, 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5, 19, 19.5, 20, 25, 30, 40, 50, 60, 70, 100, 150, 200, 250, 300, 350, 400, 500, 600, 700, 1000 13 2 2.25, 2.5, 2.75, 3, 3.25, 3.5, 3.75, 4, 4.25, 4.5, 4.75, 5, 5.25, 5.5, 5.75, 6, 6.25, 6.5, 6.75, 7, 7.25, 7.5, 7.75, 8, 8.25, 8.5, 8.75, 9, 9.25, 9.5, 9.75, 10, 10.25, 10.5, 10.75, 11, 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5, 19, 19.5, 20, 25, 30, 40, 50, 60, 70, 100, 150, 200, 250, 300, 350, 400, 500, 600, 700, 1000 14 2.25 2.5, 2.75, 3, 3.25, 3.5, 3.75, 4, 4.25, 4.5, 4.75, 5, 5.25, 5.5, 5.75, 6, 6.25, 6.5, 6.75, 7, 7.25, 7.5, 7.75, 8, 8.25, 8.5, 8.75, 9, 9.25, 9.5, 9.75, 10, 10.25, 10.5, 10.75, 11, 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5, 19, 19.5, 20, 25, 30, 40, 50, 60, 70, 100, 150, 200, 250, 300, 350, 400, 500, 600, 700, 1000 15 2.5 2.75, 3, 3.25, 3.5, 3.75, 4, 4.25, 4.5, 4.75, 5, 5.25, 5.5, 5.75, 6, 6.25, 6.5, 6.75, 7, 7.25, 7.5, 7.75, 8, 8.25, 8.5, 8.75, 9, 9.25, 9.5, 9.75, 10, 10.25, 10.5, 10.75, 11, 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5, 19, 19.5, 20, 25, 30, 40, 50, 60, 70, 100, 150, 200, 250, 300, 350, 400, 500, 600, 700, 1000 16 2.75 3, 3.25, 3.5, 3.75, 4, 4.25, 4.5, 4.75, 5, 5.25, 5.5, 5.75, 6, 6.25, 6.5, 6.75, 7, 7.25, 7.5, 7.75, 8, 8.25, 8.5, 8.75, 9, 9.25, 9.5, 9.75, 10, 10.25, 10.5, 10.75, 11, 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5, 19, 19.5, 20, 25, 30, 40, 50, 60, 70, 100, 150, 200, 250, 300, 350, 400, 500, 600, 700, 1000 17 3 3.25, 3.5, 3.75, 4, 4.25, 4.5, 4.75, 5, 5.25, 5.5, 5.75, 6, 6.25, 6.5, 6.75, 7, 7.25, 7.5, 7.75, 8, 8.25, 8.5, 8.75, 9, 9.25, 9.5, 9.75, 10, 10.25, 10.5, 10.75, 11, 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5, 19, 19.5, 20, 25, 30, 40, 50, 60, 70, 100, 150, 200, 250, 300, 350, 400, 500, 600, 700, 1000 18 3.25 3.5, 3.75, 4, 4.25, 4.5, 4.75, 5, 5.25, 5.5, 5.75, 6, 6.25, 6.5, 6.75, 7, 7.25, 7.5, 7.75, 8, 8.25, 8.5, 8.75, 9, 9.25, 9.5, 9.75, 10, 10.25, 10.5, 10.75, 11, 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5, 19, 19.5, 20, 25, 30, 40, 50, 60, 70, 100, 150, 200, 250, 300, 350, 400, 500, 600, 700, 1000 19 3.5 3.75, 4, 4.25, 4.5, 4.75, 5, 5.25, 5.5, 5.75, 6, 6.25, 6.5, 6.75, 7, 7.25, 7.5, 7.75, 8, 8.25, 8.5, 8.75, 9, 9.25, 9.5, 9.75, 10, 10.25, 10.5, 10.75, 11, 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5, 19, 19.5, 20, 25, 30, 40, 50, 60, 70, 100, 150, 200, 250, 300, 350, 400, 500, 600, 700, 1000 20 3.75 4, 4.25, 4.5, 4.75, 5, 5.25, 5.5, 5.75, 6, 6.25, 6.5, 6.75, 7, 7.25, 7.5, 7.75, 8, 8.25, 8.5, 8.75, 9, 9.25, 9.5, 9.75, 10, 10.25, 10.5, 10.75, 11, 11.25, 11.5, . 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5, 19, 19.5, 20, 25, 30, 40, 50, 60, 70, 100, 150, 200, 250, 300, 350, 400, 500, 600, 700, 1000 21 4 4.25, 4.5, 4.75, 5, 5.25, 5.5, 5.75, 6, 6.25, 6.5, 6.75, 7, 7.25, 7.5, 7.75, 8, 8.25, 8.5, 8.75, 9, 9.25, 9.5, 9.75, 10, 10.25, 10.5, 10.75, 11, 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5, 19, 19.5, 20, 25, 30, 40, 50, 60, 70, 100, 150, 200, 250, 300, 350, 400, 500, 600, 700, 1000 22 4.5 4.75, 5, 5.25, 5.5, 5.75, 6, 6.25, 6.5, 6.75, 7, 7.25, 7.5, 7.75, 8, 8.25, 8.5, 8.75, 9, 9.25, 9.5, 9.75, 10, 10.25, 10.5, 10.75, 11, 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5, 19, 19.5, 20, 25, 30, 40, 50, 60, 70, 100, 150, 200, 250, 300, 350, 400, 500, 600, 700, 1000 23 5 5.25, 5.5, 5.75, 6, 6.25, 6.5, 6.75, 7, 7.25, 7.5, 7.75, 8, 8.25, 8.5, 8.75, 9, 9.25, 9.5, 9.75, 10, 10.25, 10.5, 10.75, 11, 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5, 19, 19.5, 20, 25, 30, 40, 50, 60, 70, 100, 150, 200, 250, 300, 350, 400, 500, 600, 700, 1000 24 6 6.25, 6.5, 6.75, 7, 7.25, 7.5, 7.75, 8, 8.25, 8.5, 8.75, 9, 9.25, 9.5, 9.75, 10, 10.25, 10.5, 10.75, 11, 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5, 19, 19.5, 20, 25, 30, 40, 50, 60, 70, 100, 150, 200, 250, 300, 350, 400, 500, 600, 700, 1000 25 7 7.25, 7.5, 7.75, 8, 8.25, 8.5, 8.75, 9, 9.25, 9.5, 9.75, 10, 10.25, 10.5, 10.75, 11, 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5, 19, 19.5, 20, 25, 30, 40, 50, 60, 70, 100, 150, 200, 250, 300, 350, 400, 500, 600, 700, 1000 26 8 8.25, 8.5, 8.75, 9, 9.25, 9.5, 9.75, 10, 10.25, 10.5, 10.75, 11, 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5, 19, 19.5, 20, 25, 30, 40, 50, 60, 70, 100, 150, 200, 250, 300, 350, 400, 500, 600, 700, 1000 27 9 9.25, 9.5, 9.75, 10, 10.25, 10.5, 10.75, 11, 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5, 19, 19.5, 20, 25, 30, 40, 50, 60, 70, 100, 150, 200, 250, 300, 350, 400, 500, 600, 700, 1000 28 10 10.25, 10.5, 10.75, 11, 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5, 19, 19.5, 20, 25, 30, 40, 50, 60, 70, 100, 150, 200, 250, 300, 350, 400, 500, 600, 700, 1000 29 11 11.25, 11.5, 11.75, 12, 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5, 19, 19.5, 20, 25, 30, 40, 50, 60, 70, 100, 150, 200, 250, 300, 350, 400, 500, 600, 700, 1000 30 12 12.25, 12.5, 12.75, 13, 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5, 19, 19.5, 20, 25, 30, 40, 50, 60, 70, 100, 150, 200, 250, 300, 350, 400, 500, 600, 700, 1000 31 13 13.25, 13.5, 13.75, 14, 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5, 19, 19.5, 20, 25, 30, 40, 50, 60, 70, 100, 150, 200, 250, 300, 350, 400, 500, 600, 700, 1000 32 14 14.25, 14.5, 14.75, 15, 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5, 19, 19.5, 20, 25, 30, 40, 50, 60, 70, 100, 150, 200, 250, 300, 350, 400, 500, 600, 700, 1000 33 15 15.25, 15.5, 16, 16.5, 17, 17.5, 18, 18.5, 19, 19.5, 20, 25, 30, 40, 50, 60, 70, 100, 150, 200, 250, 300, 350, 400, 500, 600, 700, 1000

Advantageously the number of discharge cycles and recharge cycles is in the range s–t where s is selected from the group consisting of a value presented in the column headed “s” in Table E below at one of entries 1–14, and t is selected from the group of the values presented in the column headed “t” adjacent the corresponding “s” entry.

TABLE E Entry s t 1 1 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 80, 100, 150, 200, 300, 500, 750, 1000, 2500, 5000, 10000, 15000, 20000, 25000, 30000, 50000, 75000, 100000, 500000, 1000000 2 5 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 80, 100, 150, 200, 300, 500, 750, 1000, 2500, 5000, 10000, 15000, 20000, 25000, 30000, 50000, 75000, 100000, 500000, 1000000 3 10 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 80, 100, 150, 200, 300, 500, 750, 1000, 2500, 5000, 10000, 15000, 20000, 25000, 30000, 50000, 75000, 100000, 500000, 1000000 4 15 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 80, 100, 150, 200, 300, 500, 750, 1000, 2500, 5000, 10000, 15000, 20000, 25000, 30000, 50000, 75000, 100000, 500000, 1000000 5 20 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 80, 100, 150, 200, 300, 500, 750, 1000, 2500, 5000, 10000, 15000, 20000, 25000, 30000, 50000, 75000, 100000, 500000, 1000000 6 25 30, 35, 40, 45, 50, 55, 60, 65, 70, 80, 100, 150, 200, 300, 500, 750, 1000, 2500, 5000, 10000, 15000, 20000, 25000, 30000, 50000, 75000, 100000, 500000, 1000000 7 30 35, 40, 45, 50, 55, 60, 65, 70, 80, 100, 150, 200, 300, 500, 750, 1000, 2500, 5000, 10000, 15000, 20000, 25000, 30000, 50000, 75000, 100000, 500000, 1000000 8 35 40, 45, 50, 55, 60, 65, 70, 80, 100, 150, 200, 300, 500, 750, 1000, 2500, 5000, 10000, 15000, 20000, 25000, 30000, 50000, 75000, 100000, 500000, 1000000 9 40 45, 50, 55, 60, 65, 70, 80, 100, 150, 200, 300, 500, 750, 1000, 2500, 5000, 10000, 15000, 20000, 25000, 30000, 50000, 75000, 100000, 500000, 1000000 10 45 50, 55, 60, 65, 70, 80, 100, 150, 200, 300, 500, 750, 1000, 2500, 5000, 10000, 15000, 20000, 25000, 30000, 50000, 75000, 100000, 500000, 1000000 11 50 55, 60, 65, 70, 80, 100, 150, 200, 300, 500, 750, 1000, 2500, 5000, 10000, 15000, 20000, 25000, 30000, 50000, 75000, 100000, 500000, 1000000 12 100 150, 200, 300, 500, 750, 1000, 2500, 5000, 10000, 15000, 20000, 25000, 30000, 50000, 75000, 100000, 500000, 1000000 13 500 750, 1000, 2500, 5000, 10000, 15000, 20000, 25000, 30000, 50000, 75000, 100000, 500000, 1000000 14 1000 2500, 5000, 10000, 15000, 20000, 25000, 30000, 50000, 75000, 100000, 500000, 1000000

In the all-vanadium battery of the invention the catholyte may be a stabilised all-vanadium electrolyte solution. The vanadium ions in the catholyte may be stabilised at up to and including a supersaturated concentration.

In the all-vanadium battery of the invention the anolyte may be a stabilised all-vanadium electrolyte solution. The vanadium ions in the anolyte may be stabilised at up to and including a supersaturated concentration.

In the all-vanadium battery of the invention the anolyte and catholyte may be stabilised all-vanadium electrolyte solutions. The vanadium ions in the anolyte and the catholyte may be stabilised at up to and including a supersaturated concentration.

In the methods of the invention that use two stabilising agents the second stabilising agent may be the same as or different from the first stabilising agent.

In the methods of the invention the concentration of vanadium redox ions in the solution may be further increased by removing water (eg by evaporation, vacuum evaporation, pervaporation) from the solution containing the required concentration of vanadium ions in the solution.

In the methods of the invention a concentrate comprising vanadium redox ions in the solution may be formed by removing water from the solution containing the required concentration of vanadium ions in the solution and further comprising adding water to the concentrate in an amount whereby the vanadium redox ions are at a predetermined concentration in the solution.

In the methods of the invention that use two substances the first substance may different from the second substance. Typically the first substance is the same as the second substance and is selected from vanadium pentoxide, ammonium metavanadate, V₂O₃, V₂O₄, and VOSO₄.

Also disclosed are stabilized supersaturated vanadium electrolyte solutions for use in an all-vanadium redox battery comprising vanadium redox ions V(II), V(III) and/or V(IV) ions at above saturated concentrations in the negative ½-cell of the battery and V(III), V(IV) and/or V(V) ions at above saturated concentrations in the positive ½-cell of the battery, each with a supporting aqueous electrolyte typically comprising 0.5–10M H₂SO₄ and a stabilising amount of a stabilising agent wherein the stabilising amount of the stabilising agent is less than that required to fully complex the vanadium redox ions in the electrolyte solution and is sufficient to reduce precipitation of the vanadium redox ions from the stabilised electrolyte solution to a rate whereby the stabilised all-vanadium electrolyte solution is acceptable for use in an all-vanadium redox battery.

Also disclosed are stabilized supersaturated vanadium electrolyte solutions for use in an all-vanadium redox battery comprising vanadium redox ions V(II), V(III) and/or V(IV) ions at above saturated concentrations in the negative ½-cell of the battery and V(III), V(IV) and/or V(V) ions at above saturated concentrations in the positive ½-cell of the battery, each with a supporting aqueous electrolyte typically of 0.5–10M H₂SO₄ and a stabilising amount of a stabilising agent wherein the stabilising amount of the stabilising agent is less than that required to fully complex the vanadium redox ions in the electrolyte solution and is sufficient to reduce precipitation of the vanadium ions from the up to and including stabilized supersaturated concentration of vanadium redox ions to a rate which is acceptable for long term stability on standing in the temperature range 20–30° C.

Also disclosed are stabilized 1.801 –2.5 molar, typically 2 molar, vanadium redox ion containing electrolyte solutions for use in an all-vanadium redox battery comprising vanadium redox ions V(II), V(III) and/or V(IV) ions at above saturated concentrations in the negative ½-cell and V(III), V(IV) and/or V(V) ions at above saturated concentrations in the ½-cell, each with a supporting electrolyte solution typically of 0.5–12M H₂SO₄ and a stabilising amount of a stabilising agent wherein the stabilising amount of the stabilising agent is less than that required to fully complex the vanadium redox ions in the electrolyte solution and is sufficient to reduce precipitation of the vanadium redox ions from the stabilised electrolyte solution to a rate whereby the stabilised all-vanadium electrolyte solution is acceptable for use in an all-vanadium redox battery and in particular which is acceptable for long term stability on standing in the temperature range 10–40° C.

Also disclosed are stabilized 2 molar vanadium electrolyte solutions for use in an all-vanadium redox battery comprising vanadium redox ions V(II), V(III) and/or V(IV) ions in the negative ½-cell and V(III), V(IV) and/or V(V) ions in the positive ½-cell, each with a supporting aqueous electrolyte typically of 0.5–10M H₂SO₄ and a stabilising amount of a stabilising agent wherein the stabilising amount of the stabilising agent is less than that required to fully complex the vanadium redox ions in the electrolyte solution and is sufficient to reduce precipitation of the vanadium redox ions from the stabilised electrolyte solution to a rate whereby the stabilised all-vanadium electrolyte solution is acceptable for use in an all-vanadium redox battery and in particular which is acceptable for long term stability on standing in the temperature range 0–50° C.

Also disclosed are stabilized 2–3 molar vanadium electrolyte solutions for use in an all-vanadium redox battery comprising vanadium redox ions V(II), V(III) and/or V(IV) ions in the negative ½-cell and V(III), V(IV) and/or V(V) ions in the positive ½-cell, each with a supporting aqueous electrolyte typically of 0.5–10M H₂SO₄ and a stabilising amount of a stabilising agent wherein the stabilising amount of the stabilising agent is less than that required to fully complex the vanadium redox ions in the electrolyte solution and is sufficient to reduce precipitation of the vanadium redox ions from the stabilised electrolyte solution to a rate whereby the stabilised all-vanadium electrolyte solution is acceptable for use in an all-vanadium redox battery and in particular is acceptable for long term stability on standing in the temperature range 10–40° C.

Also disclosed are stabilized 2 molar vanadium electrolyte solutions for use in an all-vanadium redox battery comprising vanadium redox ions V(II), V(III) and/or V(IV) ions in the negative ½-cell and V(III), V(IV) and/or V(V) ions in the positive ½-cell, each with a supporting aqueous electrolyte typically of 0.5–10M H₂SO₄ and a stabilising amount of a stabilising agent wherein the stabilising amount of the stabilising agent is less than that required to fully complex the vanadium redox ions in the electrolyte solution and is sufficient to reduce precipitation of the vanadium redox ions from the stabilised electrolyte solution to a rate whereby the stabilised all-vanadium electrolyte solution is acceptable for use in an all-vanadium redox battery and in particular which is acceptable for long term stability on standing in the temperature range 0–50° C.

Also disclosed are stabilized 3–4 molar supersaturated vanadium electrolyte solutions for use in an all-vanadium redox battery comprising vanadium redox ions V(II), V(III) and/or V(IV) ions in the negative ½-cell and V(III), V(IV) and/or V(V) ions in the positive ½-cell, each with a supporting electrolyte solution typically of 0.5–10M H₂SO₄ and a stabilising amount of a stabilising agent wherein the stabilising amount of the stabilising agent is less than that required to fully complex the vanadium redox ions in the electrolyte solution and is sufficient to reduce precipitation of the vanadium redox ions from the stabilised electrolyte solution to a rate whereby the stabilised all-vanadium electrolyte solution is acceptable for use in an all-vanadium redox battery.

Also disclosed are stabilized supersaturated vanadium electrolyte solutions for use in an all-vanadium redox battery comprising supersaturated vanadium redox ions V(II), V(III) and/or V(IV) ions in the negative ½-cell and supersaturated V(III), V(IV) and/or V(V) ions in the positive ½-cell, each with a supporting aqueous electrolyte typically of 0.5–10M H₂SO₄ and a stabilising amount of a stabilising agent wherein the stabilising amount of the stabilising agent is less than that required to fully complex the vanadium redox ions in the electrolyte solution and is sufficient to reduce precipitation of the vanadium redox ions from the stabilised electrolyte solution to a rate whereby the stabilised all-vanadium electrolyte solution is acceptable for use in an all-vanadium redox battery and in particular to reduce precipitation of the vanadium ions from the stabilized supersaturated vanadium electrolyte solution to a rate which is acceptable for long term stability on standing in the temperature range 20–30° C.

Also disclosed are stabilized 4–5 molar supersaturated vanadium electrolyte solutions for use in an all-vanadium redox battery comprising vanadium redox ions V(II), V(III) and/or V(IV) ions in the negative ½-cell and V(III), V(IV) and/or V(V) ions in the positive ½-cell, each with a supporting electrolyte solution typically of 0.5–10M H₂SO₄ and a stabilising amount of a stabilising agent wherein the stabilising amount of the stabilising agent is less than that required to fully complex the vanadium redox ions in the electrolyte solution and is sufficient to reduce precipitation of the vanadium redox ions from the stabilised electrolyte solution to a rate whereby the stabilised all-vanadium electrolyte solution is acceptable for use in an all-vanadium redox battery.

Also disclosed are stabilized supersaturated vanadium electrolyte solutions for use in an all-vanadium redox battery comprising vanadium redox ions V(II), V(III) and/or V(IV) ions in the negative ½-cell and V(Ill), V(IV) and/or V(V) ions in the positive ½-cell, each with a supporting electrolyte solution typically of 0.5–10M H₂SO₄ and a stabilising amount of a stabilising agent wherein the stabilising amount of the stabilising agent is less than that required to fully complex the vanadium redox ions in the electrolyte solution and is sufficient to reduce precipitation of the vanadium redox ions from the stabilised electrolyte solution to a rate whereby the stabilised all-vanadium electrolyte solution is acceptable for use in an all-vanadium redox battery and in particular to reduce precipitation of the vanadium ions from the stabilized supersaturated vanadium electrolyte solution to a rate which is acceptable for long term stability on standing in the temperature range 20–30° C.

Also disclosed are stabilized 5–12 molar supersaturated vanadium electrolyte solutions for use in an all-vanadium redox battery comprising vanadium redox ions V(II), V(III) and/or V(IV) ions in the negative ½-cell and V(III), V(IV) and/or V(V) ions in the positive ½-cell, each with a supporting aqueous electrolyte typically of 0.5–10M H₂SO₄ and a stabilising amount of a stabilising agent wherein the stabilising amount of the stabilising agent is less than that required to fully complex the vanadium redox ions in the electrolyte solution and is sufficient to reduce precipitation of the vanadium redox ions from the stabilised electrolyte solution to a rate whereby the stabilised all-vanadium electrolyte solution is acceptable for use in an all-vanadium redox battery.

Also disclosed are stabilized supersaturated vanadium electrolyte solutions for use in an all-vanadium redox battery comprising supersaturated vanadium redox ions V(II), V(III) and/or V(IV) ions in the negative ½-cell and V(III), V(IV) and/or V(V) ions in the positive ½-cell, each with a supporting aqueous electrolyte typically of 0. 5–10M H₂SO₄ and a stabilising amount of a stabilising agent wherein the stabilising amount of the stabilising agent is less than that required to fully complex the vanadium redox ions in the electrolyte solution and is sufficient to reduce precipitation of the vanadium redox ions from the stabilised electrolyte solution to a rate whereby the stabilised all-vanadium electrolyte solution is acceptable for use in an all-vanadium redox battery and in particular to reduce precipitation of the vanadium ions from the stabilized supersaturated vanadium electrolyte solution to a rate which is acceptable for long term stability on standing in the temperature range 20–30° C.

Also disclosed is a process for making stabilized supersaturated electrolyte solution by electrolytic oxidation of a suspension of V₂O₃ and/or V₂O₄ and/or VOSO₄ powder to V(V) ions at up to and including a supersaturated concentration at the anode of electrolysis cell containing a supporting aqueous electrolyte typically of 0.5–10M H₂SO₄ and stabilising amount of stabilising agent wherein the stabilising amount of the stabilising agent is less than that required to fully complex the vanadium redox ions in the electrolyte solution and is sufficient to reduce precipitation of the vanadium redox ions from the stabilised electrolyte solution to a rate whereby the stabilised all-vanadium electrolyte solution is acceptable for use in an all-vanadium redox battery. The V(II), V(III) and V(IV) redox ions are produced by reduction of V(V) in solution at up to and including a supersaturated concentration.

Also disclosed is a process for making stabilized supersaturated electrolyte solution by electrolytic reduction of V₂O₅ suspension at cathode of electrolysis cell containing supporting aqueous electrolyte typically of 0.5–10M H₂SO₄ and stabilising amount of stabilising agent and reducing for sufficient time to produce 50:50 mixture of V(III) or V(IV) (V^(3.5)) which is then placed into both sides of VRB and charged to V(II) and V(V) states respectively or left in discharged form of V(III) and V(IV) respectively until needed, wherein the stabilising amount of the stabilising agent is less than that required to fully complex the vanadium redox ions in the electrolyte solution and is sufficient to reduce precipitation of the vanadium redox ions from the stabilised electrolyte solution to a rate whereby the stabilised all-vanadium electrolyte solution is acceptable for use in an all-vanadium redox battery.

Also disclosed is a process for making stabilized supersaturated V^(3.5+) electrolyte solution by concentrating a 2M V^(3.5+) solution containing a stabilizing agent by boiling or pervaporation or applying vacuum and/or heat to remove required amount of water wherein the stabilising amount of the stabilising agent is less than that required to fully complex the vanadium redox ions in the electrolyte solution and is sufficient to reduce precipitation of the vanadium redox ions from the stabilised electrolyte solution to a rate whereby the stabilised all-vanadium electrolyte solution is acceptable for use in an all-vanadium redox battery.

Also disclosed is a process for making V^(3.5+) electrolyte solution concentrate (as suspended slurry) by the process for making stabilized supersaturated V^(3.5+) electrolyte solution; by concentrating a 2M V^(3.5+) solution by boiling or pervaporation or applying vacuum and/or heat to remove required amount of water and reconstituting by adding required amount of water to redissolve vanadium precipitate to form supersaturated solution just prior to addition to vanadium redox battery electrolyte solution tanks.

The vanadium redox ions may be stabilised at up to and including a supersaturated concentration.

Typically the negative and positive compartments are sealed air-tight.

Typically the negative and positive compartments are deaerated.

All-vanadium redox charge and discharge cells of the invention can be operated over a broad temperature range, e.g. −5° C. to 99° C. but are typically operated in the temperature range 2° C. to 65° C., or 5° C. to 45° C., and even more typically 10° C. to 40° C.

The anolyte and the catholyte comprise an electrolyte solution which is typically an aqueous solution which includes at least one of H₂SO₄, trifluoromethanesulphonic acid, Na₂SO₄, ammonium sulphate, K₂SO₄, H₃PO₄, Na₃PO₄, K₃PO₄, KNO₃, NaNO₃, sulphonic acid, C₆–C₁₄ arylsulphonic acid such as p-toluenesulphonic acid, benzenesulphonic acid, naphthalenesulphonic acid, C₁–C₆ alkylsulphonic acid such as methylsulphonic acid and ethylsulphonic acid, acetic acid or mixtures thereof in a concentration of from 0.01M to 20M, or 0.01M to 15M, 0.01M to 10M. It is especially preferred to use H₂SO₄ in a concentration of from 1.5M to 10M, more preferably 1.75M to 10M (other concentration ranges include 0.25M to 10M, 2M to 10M, 2M to 9M, 2.5M to 9M, 2.8M to 8M, 3M to 7M, 3M to 6M, 4M to 6.5M, 5.001M to 10M, 5.001M to 7.5M, 5.001M to 10M, 5.001M to 7.0M, and 5.001M to 6M). It is especially preferred to use H₂SO₄ in a concentration of from 2M to 8M, more preferably 4.5M to 8M.

The electrolyte solution typically has vanadium ions (V(II), V(III), V(IV) and/or V(V) ions in any form, (examples of forms include vanadate ions such as metavanadate, orthovanadate, pyrovanadate, as well as vanadyl ions such as vanadylous and divalent vanadyl ions) in sufficient concentration for high discharge capacity in the discharge battery, for example, up to and including a supersaturated concentration, 0.001 to 15M, 0.1M to 12M, 0.25M to 10M, 2M to 10M, 2M to 9M, 2.5M to 9M, 2.8M to 8M, 3M to 7M, 3M to 6M, 4M to 6.5M, 5.001M to 10M, 5.001M to 7.5M, 5.001M to 10M, 5.001M to 7.0M, and 5.001M to 6M are typical in the charge and discharge cells of the invention. The vanadium ions in the electrolyte solution are prepared by dissolving an oxide, sulphate, phosphate, nitrate, halogenide or other salt or complex of vanadium which is soluble or which can be solubilized in the electrolyte solution. Examples of suitable vanadium salts include ammonium metavanadate (NH₄VO₃); ammonium vanadium sulphate (NH₄V(SO₄)₂); barium pyrovanadate (Ba₂V₂O₇); bismuth vanadate (Bi₂O₃ V₂O₅); cesium vanadium sulphate (VCs(SO₄)₂ 12H₂O); iron metavanadate (Fe(VO₂)₃); lead metavanadate (Pb(VO₅)₂); potassium metavanadate (KVO₃); potassium vanadium sulphate (KVSO₄); rubidium vanadium sulphate (RbV(SO₄)₂); sodium metavanadate (NaVO₃); metavanadic acid (HVO₃); sodium orthovanadate (Na₃VO₄); potassium orthovanadate (K₃VO₄); ammonium orthovanadate; sodium pyrovanadate (Na₄V₂O₇); potassium pyrovanadate (K₄V₂O₇); ammonium pyrovanadate; sodium hexavanadate (Na₄V₆O₁₇); potassium hexavanadate (K₄V₆O₁₇); ammonium hexavanadate; thallium pyrovanadate (Tl₄V₂O₇); thallium metavanadate (TIVO₃); thallium pyrovanadate (TIV₂O₇ 6H₂O); vanadium pentoxide (V₂O₅); vanadium sulphate (V(SO₄)₂); vanadium sulphate (V₂(SO₄)₂); vanadium oxide VO; and calcium and magnesium vanadates including calcium metavanadate and magnesium metavanadate. Other vanadium salts and complexes can also be dissolved and reduced in an electrolyte solution. Generally for an all-vanadium redox battery, the catholyte and anolyte include a solution of vanadium prepared from a salt selected from the group consisting of a salt of the formula VO(X)_(y) where y is 2 and X is F, Br or Cl, a salt of the formula VO(X)_(y) where y is 1 and X is SO₄ or O, V₂O₅, V₂O₃, V₂O₄, VSO₄, V₂(SO₄)₃, (VO₂)₂SO₄, and NH₄VO₃. Vanadium salts or complexes such as ammonium metavanadate (NH₄VO₃), V₂O₅, V₂O₃, V₂O₄, VSO₄, V₂(SO₄)₃, VOSO₄ and ammonium vanadium sulphate (NH₄V(SO₄)₂) are particularly advantageous since no additional ions other than vanadium sulphate and ammonium are introduced permitting higher concentrations of vanadium ions to be prepared and reducing further treatment of electrolyte solution to remove unwanted products. It is especially preferable to dissolve vanadyl sulphate in 0.5M to 10M, more typically 3 to 9M, and even more typically 4 to 8M and yet even more typically 5 to 7.5M H₂SO₄ or V₂O₅ or ammonium metavanadate in 0.5M to 10M, more typically 3 to 9M, and even more typically 4 to 8M and yet even more typically 5 to 7.5M H₂SO₄ by electrolytic dissolution or by chemical leaching with V(III) or other suitable reductant (see e.g. International Application No. PCT/AU88/00471 the contents of which are incorporated herein by cross reference).

The stabilising agent is selected in accordance with the types of redox ions involved. Depending on those ions the stabilising agent may be K₂SO₄, Na₂SO₄, KHC₂O₄.H₂O, K₂C₂O₄, Na₂C₂O₄, (NH₄)₂C₂O₄, NH₄HC₂O₄.H₂O, LiHC₂O₄.H₂O, NaHC₂O₄.H₂O, Li₂C₂O₄, H₂C₂O₄. Other stabilising agents can be used. For example, in principle it should possible to use a reducing organic water-soluble compound such as a reducing organic water-soluble mercapto group-containing compound including SH-containing water-soluble lower alcohols (including SH-containing C₁–C₁₂ primary, secondary and tertiary alkyl alcohols), SH-containing C₁–C₁₂ primary, secondary and tertiary alkyl carboxylic acids, SH-containing C₁–C₁₂ primary, secondary and tertiary alkyl amines and salts thereof, SH-containing C₁–C₁₂ primary, secondary and tertiary alkyl amine acids and dior tripeptides such as 2-mercaptoethylamine hydrochloride, 2-mercaptoethanol, 2-mercaptopropionylglycine, 2-mercaptopropionic acid, cystenylglycine, cysteine, carbamoyl cysteine, homocysteine, glutathione, cysteine hydrochloride ethyl ester and acetylcysteine. Further examples of stabilising agents may be found in PCT/AU94/00711, the contents of which are incorporated herein by cross reference.

The stabilising agent may be a surfactant. The surfactant may be an anionic, cationic, amphoteric or nonionic surfactant. Mixtures of surfactants may be used but some surfactants are incompatible such as a mixture of anionic and cationic surfactants.

Examples of anionic surfactants are water-soluble soaps or water-soluble synthetic surface active compounds. Examples of soaps are unsubstituted or substituted ammonium salts of higher fatty acids (C₁₀–C₂₂), such as sodium or potassium salts of oleic acid or stearic acid or of natural fatty acid mixtures such as coconut oil or tallow oil, alkali metal salts, alkaline earth metal salts or fatty acid methyllaurin salts. Examples of synthetic surfactants are alkylarylsulphonates, sulphonated benzimidazole derivatives, fatty alcohol sulphates, or fatty alcohol sulphonates.

Examples of alkylarylsulphonates are calcium, sodium or triethanolamine salts of dodecylbenzenesulphonic acid, dibutylnaphthalenesulphonic acid, or of a condensate of naphthalenesulphonic acid and formaldehyde or the phosphate salt of the phosphoric acid ester of an adduct of p-nonylphenol with 4 to 14 moles of ethylene oxide. Examples of sulphonated benzimidazole derivatives are 2 sulphonic acid groups and one fatty acid radical containing approximately 8 to 22 carbon atoms. Examples of fatty alcohol sulphates or sulphonates are unsubstituted or substituted ammonium salts such as C₈–C₂₂ alkyl radical including the alkyl moiety of acyl radicals such as the calcium or sodium salt of lignosulphonic acid, of a mixture of fatty alcohol sulphates from naturally occurring fatty acids, of dodecylsulphate, alkali metal salts or alkaline earth metal salts or the salts of sulphated and sulphonated fatty alcohol/ethylene oxide adducts.

Examples of non-ionic surfactants are polyglycol ether derivatives of aliphatic or cycloaliphatic alcohols having approximately 3 to 30 glycol ether groups and approximately 8 to 20 carbon atoms in the (aliphatic) hydrocarbon moiety; saturated or unsaturated fatty acids and alkylphenols having approximately 6 to 18 carbon atoms in the alkyl moiety of the alkylphenols; water-soluble adducts of polyethylene oxide with ethylenediaminopolypropylene glycol, polypropylene glycol, or alkylpolypropylene glycol having approximately 1 to 10 carbon atoms in the alkyl chain, having approximately 20 to 250 ethylene glycol ether groups and approximately 10 to 100 propylene glycol ether groups in the usual ratio of 1 to 5 ethylene glycol moiety: propylene glycol moiety; fatty acid esters of polyoxyethylene sorbitan such as polyoxyethylene sorbitan trioleate; octylphenoxypolyethoxyethanol; polyethylene glycol; tributylphenoxypolyethyleneethanol; polypropylene/polyethylene oxide adducts; castor oil polyglycol ethers; nonylphenolpolyethoxyethanols.

Examples of cationic surfactants are quaternary ammonium salts in the form of halides, methylsulphates or ethylsulphates which have as N-substituent at least one C₈–C₂₂ alkyl radical or unsubstituted or halogenated lower alkyl or benzyl or hydroxy-lower alkyl radicals, such as stearyltrimethylammonium chloride or benzyldi(2-chloroethyl)ethylammonium bromide.

Examples of amphoteric surfactants are the aminocarboxylic and aminosulphonic acids and salts thereof such as alkali metal 3-(dodecylamino)propionate and alkali metal 3-(dodecylamino)propane-1-sulphonate or alkyl and alkylamido betaines such as cocamidopropyl betaine.

Examples of surfactants which may be used in the combination are surfactants from the Teric® series such as N4 Teric, Teric BL8, Teric 16A16, Teric PE61, alkanate 3SL3, N9 Teric, G9 A6 Teric or from the Rhodafac® series such as Rhodafac RA 600. Further examples are Calgon® (sodium hexametaphosphate), Borax® (sodium decahydrate borate), soap, sodium lauryl sulphate, or sodium cholate. Further examples of surfactants are described in “Encyclopedia of Chemical Technology”, Kirk Othmer, 3rd edition, Volume 8, John Wiley & Sons 1982, “Handbook of Surfactants”, M. R. Porter, Blackie (Glasgow and London), Chapman and Hall (USA) 1991, “Encyclopedia of Surfactants”, compiled by Michael and Irene Ash, Volumes I–III, Chemical Publishing Co. 1980–1981, “Encyclopedia of Surfactants”, compiled by Michael and Irene Ash, Volume IV, Chemical Publishing Co. 1985, “A Formulary of Detergents and Other Cleaning Agents”, compiled by Michael and Irene Ash, Chemical Publishing Co. 1980, “Emulsifying Agents An Industrial Guide”, Ernest W. Flick, Noyes Publications 1990, “What Every Chemical Technologist Wants To Know About. Volume IV Conditioners, Emollients and Lubricants”, compiled by Michael and Irene Ash, Edward Arnold 1990, “McCutcheon's Detergents and Emulsifiers Annual”, MC Publishing Corp., Glen Rock, N.J., USA, 1988 and “Tensid-Taschenbuch”, H. Stache, 2nd edition, C. Hanser Verlag, Munich, Vienna, 1981, the contents of all of which are incorporated herein by cross reference. Typically more than one surfactant is used. Generally the amount of surfactant used in the combination is 0.5 to 99 wt %, preferably 20 to 90 wt %, more preferably 50 to 80 wt %, based on the total weight of the combination.

The oxidation and reduction and other products of the above compounds are included within the definition of stabilising agent. The reason for this is that many of the above compounds listed above may be converted to other products in the electrolyte solution. For example, organic compounds may be oxidised/reduced into other compounds or may combine with the vanadium ions/compounds to form new products or the products of the above compounds may combine with vanadium ions/compounds to form new products. It may be these other products which act as stabilising agents. Thus throughout the specification and claims “stabilising agent” is to be taken to include products arising after addition of any of the above compounds or any other stabilising agent to the electrolyte solution.

Generally the stabilising agent is an inorganic phosphate, or a polyhydric alcohol, polyamine or polymercapto group containing chain or cyclic organic compound with 2 or more —OH, —NH₂ and/or SH groups or mixtures of these. Preferably these groups are in secondary or tertiary positions for improved stability to oxidation.

Generally, the stabilising agent is K₂SO₄, Na₂SO₄, potassium phosphate, sodium hexametaphosphate, sodium polyphosphate, thiourea, ammonium sulphate, urea, glycerine, a derivative of glycerine, oxalic acid or a salt of oxalic acid, such as ammonium oxalate, sodium oxalate, potassium oxalate, rubidium oxalate, caesium oxalate, magnesium oxalate, calcium oxalate or strontium oxalate, saccharide including L- and D-isomers and α and β forms, including acid-soluble monosaccharides such as glucose, fructose, mannose, an aldose including aldomonose, aldodiose, aldotriose, aldotetrose, aldopentose, aldohexose, aldoheptose, aldooctose, aldononose, and aldodecose, a ketose including ketomonose, ketodiose, ketotriose, ketotetrose, ketopentose, ketohexose, ketoheptose, ketooctose, ketononose, and ketodecose, idose, galactose, allose, arabinose, gulose, fucose, glycose, glycosulose, erythrose, threose, ribose, xylose, lyxose, altrose, idose, talose, erythrulose, ribulose, mycarose, xylulose, psicose, sorbose, tagatose, glucuronic acid, glucaric acid, gluconic acid, glucuronic acid, glyceraldehyde, glucopyranose, glucofuranose, aldehydo-glucose, arabinofuranose, galacturonic acid, manuronic acid, glucosamine, galactosamine and neuraminic acid, disaccharides such as sucrose, maltose, cellobiose, lactose, and trehalose, acid-soluble, branched or unbranched or cyclic, homo- or hetero- oligosaccharides including di-, tri-, tetra- penta-, hexa-, hepta-, octa-, nona- and deca-saccharides, cyclodextrin, cycloheptaamylose, cyclomaltoheptaose, and acid-soluble, branched or unbranched or cyclic, homo- or hetero-polysaccharides such as small starch molecules, as well as homo or heteropolymers thereof, glycosides such as ethyl glucopyranoside, D-fructose, L-fructose, D-talose, L-talose, D-ribose, L-ribose, D-altrose, L-altrose, D-lyxose, L-lyxose, D-xlose, L-xlose, D-inositol, L-inositol, L-arabinose, L-sorbose, D-glucose, L-glucose, D-galactose, L-galactose, D-mannose, L-mannose, methyl β-D-xylopyranoside, methyl β-L-xylopyranoside, D-xylose, L-xylose, β-D-galactopyranoside, β-L-galactopyranoside, methyl α-D-mannopyranoside, methyl α-D-glucopyranoside, methyl α-L-glucopyranoside, 2-deoxy-D-ribose, methyl phenyl β-D-galactopyranoside, D-mannose, L-mannose, methyl β-D-arabinopyranoside, 2-deoxy-D-galactose, and 2-deoxy-D-glucose are specific examples of such saccharides. Stabilising agents may also be a polyhydric alcohol, such as —CH₂—CHOH—CH₂OH, —CH₂—(CHOH)₂—CH₂OH, —CH₂—(CHOH)₃—CH₂—OH, —CH₂—(CHOH)₄—CH₂OH, or mannitol, sorbitol, glycidol, inositol, pentaerythritol, galacitol, adonitol, xylitol, alabitol, monosodium glutamate, ariflic acid, triethylenetetramine (TRIEN), D-penicillamine, D, L-penicillanine ascorbic acid, sodium citrate, potassium citrate, plus the following compounds or mixtures of two or more of the following compounds; numbers 6, 7, 15, 16, 17, 19, 24, 35, 40, 43, 44, 50, 51, 52, 53, 54, 55, 56, 57, 58, 60, 62, 63, 66, 67, 68, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89 from the CRC Handbook of Physics and Chemistry (1972–1973 edition) or the following compounds likewise from CRC Handbook of Physics and Chemistry (1972–73 edition) (incorporated herein by cross reference) with nos. m120, p1881, r1, r27, r55, t25p, t255, m153, a778, a782, a790, a1391, a1394, c231, c737, d186, e82, e84, e147, e148, f39, f174, f175, f176, g5, g29, g30, g33, g34, g37, g38, g41, g50, g52, g53, g54, g55, g56, g57, g214, g217, g218, 12, 13, I166, 14, 15, and 16.

Particularly desirable are K₂SO₄, urea, adonitol, allitol, D-allose, L-allose, α-altrose, ammonium oxalate, D-arabinose (α and β forms), L-arabinose (α and β forms), D-arabitol, DL-arabitol, L-arabitol, D-arabonic acid, DL-arabonic acid, L-arabonic acid, 3 methyl D-fucose, D-epifucitol, L-epifucitol, L-epifucose, β-fructose (D-), fucose, α-fucose (L-), D-galactitol, galactonic acid, D-galactose, gluco-α-heptose, glucomethylose, gluconal, D-gluconic acid, sodium gluconate, potassium gluconate, ammonium gluconate, D-glucose, D-α-glucose, D-β-glucose, α-methyl-D-glucoside, gulose, glycerine, β-methyl-D-glucoside, D-glucuronic acid, iditol, L-idonic acid, idose (D- and L-), inositol (allocis-, D-, epi-, L-, muco-, myo-, neo-, scyllo-), D-mannitol, DL-mannitol, L-mannitol, D-α-mannoheptose, D-β-mannoheptose, D-β-mannoheptose monohydrate, mannoic acid (D and 1), D-mannose, DL-mannose, DL-mannose, L-mannose, D,α-mannuronic acid, β-mannuronic acid (and Na, K and ammonium salts), mucic acid (and Na, K and ammonium salts), D-ribose, saccharic acid, scyllitol, sorbitol (D- and L-), sorbose (D-, DL- and L-), tagatose, talitol, talonic acid (and Na, K and ammonium salts), talose, xylitol, xylose, lactose, fructose, γ-lactone (and Na, K and ammonium salts), idonic acid (and Na, K and ammonium salts), ammonium gluconate, or mixtures of 2 or more of the foregoing.

Typically the stabilising agent is at least one compound selected from the group consisting of (i) substituted ring carbon compounds (aryl and alkyl and alkenyl) containing 3 or more (typically 3–15, more typically 3–10) carbon atoms including at least two groups selected from the group consisting of —OH, ═O, —COOH, —NH₂, and —SH, (ii) C₂–C₁₂ primary, secondary or tertiary carbon chain compounds selected from the group consisting of C₂–C₁₂ alkyl, C₂–C₁₂ alkenyl, and C₂–C₁₂ alkynyl, the carbon chain compound including at least two groups selected from the group consisting of —OH, ═O, —COOH, —NH₂, and —SH, (iii) ring or chain polyphosphates containing at least 2 P atoms, optionally 2–12 P atoms, and including at least two groups selected from the group consisting of —OH and ═O, (iv) polyphosphonates, (v) lactose, sorbitol, fructose, glucose, inositol, myo-inositol, glycerine, tartaric acid, asparagine, sodium tripolyphosphate, sodium hexametaphosphate, sodium acid pyrophosphate, nitrilotris(methylene-phosphonic acid), potassium nitrilotris (methylenephosphonate) N-oxide, and sodium nitrilo-tris(methylenephosphonate), (vi) sugars, (vii) carbohydrates, (viii) amino acids, (ix) ammonium compounds.

More typically for vanadium ions, the stabilising agent is K₂SO₄, Na₂SO₄, urea, postassium phosphate, ammonium sulphate, ammonium oxalate, glycerine, sodium gluconate, galactose, galactitol, γ-lactone (and Na and K salt), idose, idonic acid (and Na and K salt), iditol, mannose, mannitol, mannonic acid (and Na and K salt), sorbitol, inositol, fructose, fucose, triethylenetetramine, Li₂SO₄, aluminium sulphate, thiourea, asparagine, glycine, citric acid, ammonium carbonate, sodium polyphosphate, sodium pentapolyphosphate, sodium tripolyphosphate, sodium hexametaphosphate, potassium persulphate, Briquest, polystyrene sulphonic acid, or mixtures of 2 or more of these. A mixture of inorganic and organic stabilising agents may be used.

The stabilising agent in the anolyte may be the same as the stabilising agent in the catholyte. Alternatively, the stabilising agent in the anolyte may be different from the stabilising agent in the catholyte.

The stabilising agent may be used in an amount ranging from 0.0001% to 40% or 0.01% to 20% wt/vol wt/vol (in the case of solids, for example) or wt/wt (i.e. wt of stabilising agent:wt of solution or wt of stabilising agent:wt of redox ions being stabilised) or vol/vol (i.e. vol of stabilising agent:vol of solution) or vol/wt (i.e. vol of stabilising agent:wt of solution or vol of stabilising agent:wt of redox ions being stabilised) in the case of stabilising agents that are liquids,) or mole/mole (i.e. mole of stabilising agent:mole of redox ions being stabilised) for example. Typically, the stabilising agent is used in an amount of from 0.05% to 20%, more typically 0.1% to 10%, even more typically 0.5% to 8%, and even more typically 0.5% to 7% wt/vol or wt/wt or vol/vol or vol/wt. A stabilising amount of stabilising agent is generally less than the amount required to completely chelate or complex all the redox ions or redox couple(s) present in solution. That is, typically the stabilising agent is present in an amount that is a molar fraction of the amount of stabilising that would be required to completely chelate or complex all the redox ions or redox couple(s) present in solution (e.g. <20% mole/mole of stabilising agent:redox ions or redox couple(s)). Even more typically, the stabilising agent is used in an amount of from 0.25% to 5%. Yet more typically, the stabilising agent is used in an amount of from 0.5% to 3%. An effective stabilising amount of a stabilising agent can be added to the vanadium containing electrolyte solution prior to, during or after the preparation of a vanadium redox electrolyte solution. The desired amount of stabilising agent for a given redox ion will be readily ascertained by a person skilled in the art without undue experimentation. Thus the stabilising agent is typically used in one of the following ranges: 0.01% to 20% wt/vol, 0.01% to 20% wt/wt, 0.01% to 20% vol/vol, 0.01% to 20% vol/wt, 0.01% to 20% mole/mole, 0.05% to 20% wt/vol, 0.05% to 20% wt/wt, 0.05% to 20% vol/vol, 0.05% to 20% vol/wt, 0.05% to 20% mole/mole, 0.1% to 10% wt/vol, 0.1% to 10% wt/wt, 0.1% to 10% vol/vol, 0.1% to 10% vol/wt, 0.1% to 10% mole/mole, 0.5% to 8% wt/vol, 0.5% to 8% wt/wt, 0.5% to 8% vol/vol, 0.5% to 8% vol/wt, 0.5% to 8% mole/mole, 0.5% to 5% wt/vol, 0.5% to 5% wt/wt, 0.5% to 5% vol/vol, 0.5% to 5% vol/wt, 0.5% to 5% mole/mole, 0.75% to 3% wt/vol, 0.75% to 3% wt/wt, 0.75% to 3% vol/vol, 0.75% to 3% vol/wt, 0.75% to 3% mole/mole, 1% to 2% wt/vol, 1% to 2% wt/wt, 1% to 2% vol/vol, 1% to 2% vol/wt or 1% to 2% mole/mole.

The cells and batteries of the invention may be constructed according to generally known methods for construction of redox cells.

The electrochemical reactions of the redox cell can be conducted in any electrochemical cell which has an anode compartment and a cathode compartment through which the appropriate fluids can be transported. A particular redox cell in which the stabilising agents may be used to particular advantage is an all-vanadium battery described in U.S. Pat. No. 4,786,567, the contents of which are incorporated herein by cross reference (but unexpectedly and surprisingly with vanadium ion concentrations up to 10M).

The electrochemical cell is typically a cell of the “membrane-type”, that is it employs a membrane rather than a diaphragm to separate a positive compartment from a negative compartment. Preferred embodiments for the said membrane, the design of the anode and cathode compartments of the redox cell, and electrode materials, construction and arrangement are as described hereinbefore under the heading “Summary of Invention”

Other methods of dissolving V₂O₅ and other vanadium salts are disclosed below. The methods described herein can be readily be modified to take advantage of the present invention by adding an effective stabilising amount of a stabilising agent to the vanadium containing electrolyte solution prior to, during or after the preparation of a vanadium redox electrolyte solution.

According to another embodiment of this invention there is provided a process for producing a stabilized vanadium electrolyte solution, above saturated concentration, by dissolving and reducing a reducible vanadium compound disposed in, but not wholly dissolved in, an aqueous electrolyte containing a stabilizing amount of a stabilizing agent by utilizing an electrochemical cell which aqueous electrolyte is in electrical contact with a positive electrode and a negative electrodes to dissolve and reduce at least a part of the compound in the electrolyte solution.

According to a further embodiment of this invention there is provided a process for producing a stabilized vanadium electrolyte solution, above saturated concentration, by dissolving and reducing a reducible vanadium compound disposed in, but not wholly dissolved in, an aqueous electrolyte containing a stabilizing amount of a stabilizing agent by utilizing an electrochemical cell having a positive compartment containing a catholyte in electrical contact with a positive electrode, a negative compartment containing an anolyte comprising an aqueous electrolyte in electrical contact with a negative electrode, and an ionically conducting separator disposed between the positive and negative compartments and in contact with the catholyte and the anolyte to provide ionic communication therebetween which process comprises adding the vanadium compound to the aqueous electrolyte or wherein the vanadium compound is predisposed in the aqueous electrolyte, and providing electrical energy from an external circuit to the positive and negative electrodes to dissolve and and reduce at least a part of the compound in the aqueous electrolyte.

The aqueous electrolyte can include vanadium (II) and/or vanadium (III) ions disposed therein. The vanadium compound is thus reduced and dissolved by the V(II)/V(III) ions in the presence of a stabilizing amount of a stabilizing agent on addition to the aqueous solution and resultant V(IV) ions can be reduced at the negative electrode to V(II)/V(III) ions. Generally above saturated concentrations, or 0.1 to 15M, or 0.05 to 10M typically 0.25M to 5M V(II)/V(III) ions are included in the aqueous electrolyte. (By V(II)/V(III) is meant V(II) ions alone or V(III) alone or a mixture of V(II) and V(III) ions).

According to another embodiment of this invention there is provided a process for producing a stabilized vanadium electrolyte solution, above saturated concentration, by dissolving and reducing a reducible vanadium compound disposed in, but not wholly dissolved in, an aqueous electrolyte containing a stabilizing amount of a stabilizing agent which process comprises adding a chemical reductant to the electrolyte solution to dissolve and reduce the compound in the electrolyte solution.

According to a further embodiment of this invention there is provided a process for producing a stabilized vanadium electrolyte solution, above saturated concentration, by dissolving and reducing a reducible vanadium compound disposed in, but not wholly dissolved in, an aqueous electrolyte containing a stabilizing amount of a stabilizing agent by utilizing a chemical reductant and an electrochemical cell having the aqueous electrolyte in electrical contact with a positive electrode and a negative electrode which process comprises:

(a) adding a chemical reductant to the electrolyte solution to assist in dissolution and reduction of the compound in the electrolyte solution; and

(b) providing electrical energy from an external circuit to the positive and negative electrodes to dissolve and reduce at least a part of the compound in the electrolyte solution.

According to another embodiment of this invention there is provided a process for producing a stabilized vanadium electrolyte solution, above saturated concentration, by dissolving and reducing a reducible vanadium compound disposed in, but not wholly dissolved in, an aqueous electrolyte containing a stabilizing amount of a stabilizing agent by utilizing a chemical reductant and an electrochemical cell having a positive compartment containing a catholyte in electrical contact with a positive electrode, a negative compartment containing an anolyte comprising the aqueous electrolyte in electrical contact with a negative electrode, and an ionically conducting separator disposed between the positive and negative compartments and in contact with the catholyte and the anolyte to provide ionic communication therebetween which process comprises:

(a) adding a chemical reductant to the anolyte to assist in dissolution and reduction of the compound in the anolyte; and

(b) providing electrical energy from an external circuit to the positive and negative electrodes to dissolve and reduce at least a part of the compound in the electrolyte solution.

Alternative processes for the preparation of a stabilised vanadium electrolyte solution, optionally highly supersaturated with vanadium ions can be performed by adapting the processes described in AU85862/91, the contents of which are incorporated by cross reference, by adding a stabilizing agent to the electrolyte solution during or prior to the preparation of the vanadium electrolyte solution.

The chemical reductant can be a V(II), V(III) or V(IV) compound, which is soluble in the electrolyte solution or an aqueous solution containing V(II), V(III) and/or V(IV) ions, particularly an aqueous solution of VOSO₄ dihydrate, hydrated (V₂(SO₄)₃) and/or VSO₄.7H₂O, in an amount sufficient to dissolve and reduce the vanadium compound. It is particularly preferred that a V(II) or V(III) compound, or the the aqueous solution contains V(II) and/or V(III) ions.

The chemical reductant may also be KHC₂O₄.H₂O, K₂C₂O₄, Na₂C₂O₄, (NH₄)₂C₂O₄NH₄HC₂O₄.H₂O, LiHC₂O₄.H₂O, NaHC₂O₄.H₂O, Li₂C₂O₄, SO₂, H₂C₂O₄, H₂SO₃, NaHSO₃, Na₂SO₃, Na₂S₂O₃, Na₂S₂O₄, Na₂S₂O₅, Na₂S₂O₆, Li₂SO₃, Li₂SO₆, KHSO₃, K₂SO₃, K₂S₂O₃, K₂S₂O₄, K₂S₂O₅, K₂S₂O₆, NH₄HSO₃, (NH₄)₂SO₃, (NH₄)₂SO₄, (NH₄)₂SO₅, N₂H₄, H₂N₂H₂.H₂O, H₂N₂H₂.H₂SO₄, (NH₄)₂SO₆, NaBH₄, LiBH₄, KBH₄, Be(BH₄)₂, D₂, T₂, S, H₂O₂, hydrazine, sulphurous acid, hydrazine dihydrochloride, hydrogen peroxide, CaH₂, MgH₂, H₂ or calcium and magnesium salts of sulphurous acid, alkali-hydrogen-phosphites (Li, K, Na), alkali hypophosphites (Li, K, Na), hydroxyl amines, pyrosulphurous acid and dithioneous acid. Other chemical reductants can be used. For example, in principle it should be possible to use a reducing organic water-soluble compound such as a reducing organic water-soluble mercapto-group containing compound including SH-containing water-soluble lower alcohols (including SH-containing C₁–C₁₂ primary, secondary and tertiary alkyl alcohols), SH-containing C₁–C₁₂ primary, secondary and tertiary alkyl carboxylic acids, SH-containing C₁–C₁₂ primary, secondary and tertiary alkyl amines and salts thereof, SH-containing C₁–C₁₂ primary, secondary and tertiary alkyl amine acids and dior tripeptides such as 2-mercaptoethylamine hydrochloride, 2-mercaptoethanol, 2-mercaptopropionylglycine, 2-mercaptopropionic acid, cystenylglycine, cysteine, carbamoyl cysteine, homocysteine, glutathione, cysteine hydrochloride ethyl ester and acetylcysteine. In principle it should also be possible to employ photocatalytic reduction and photoreduction at a semiconductor photocathode.

Reductants such as (NH₄)₂C₂O₄NH₄HC₂O₄.H₂O, SO₂, S, H₂O₂, H₂C₂O₄, NH₄HSO₃, (NH₄)₂SO₃, (NH₄)₂SO₄, (NH₄)₂SO₅, N₂H₄, H₂N₂H₂.H₂O, H₂N₂H₂.H₂SO₄, (NH₄)₂SO₆ and H₂ are particularly advantageous as reductants since at least some of the reaction product is gaseous permitting higher concentrations of vanadium ions to be prepared and reducing further treatment of electrolyte solution to remove unwanted products.

The vanadium compound can be ammonium metavanadate (NH₄VO₃); ammonium vanadium sulphate (NH₄V(SO₄)₂); barium pyrovanadate (Ba₂V₂O₇); bismuth vanadate (Bi₂O₃ V₂O₅); cesium vanadium sulphate (VCs(SO₄)₂ 12H₂O); iron metavanadate (Fe(VO₂)₃); lead metavanadate (Pb(VO₅)₂); potassium metavanadate (KVO₃); potassium vanadium sulphate (KVSO₄); rubidium vanadium sulphate (RbV(SO₄)₂); sodium metavanadate (NaVO₃); metavanadic acid (HVO₃); sodium orthovanadate (Na₃VO₄); sodium pyrovanadate (Na₄V₂O₇); sodium hexavanadate (Na₄V₆O₁₇); thallium pyrovanadate (Tl₄V₂O₇); thallium metavanadate (TlVO₃); thallium pyrovanadate (TIV₂O₇ 6H₂O); vanadium pentoxide (V₂O₅); vanadium sulphate (V(SO₄)₂); V₂O₃, V₂O₄, VO₂, VO and calcium and magnesium vanadates including calcium metavanadate and magnesium metavanadate. Other vanadium salts and complexes can also be dissolved and reduced in an electrolyte solution by the processes of the invention. For example, in principle it should also be possible to produce highly supersaturated stabilized vanadium electrolyte solutions containing stabilizing agents by dissolving and reducing vanadium salts occurring in vanadium-bearing minerals such as patronite, bravoite, sulvanite, davidite, roscoelite, carnotite, vanadinite, descloizite, cuprodescloizite, vanadiferous phosphate rock and titaniferous magnetite using the processes of the invention as well as for recovering vanadium from spent catalysts and fly-ash.

Vanadium salts or complexes such as ammonium metavanadate (NH₄VO₃) and ammonium vanadium sulphate (NH₄V(SO₄)₂) V₂O₅, V₂O₃, V₂O₄, VO₂, are particularly advantageous since they permit higher concentrations of vanadium ions to be prepared and reduce further treatment of electrolyte solution to remove unwanted products.

The electrolyte typically comprises an aqueous solution which includes H₂SO₄, trifluoromethanesulphonic acid, Na₂SO₄, K₂SO₄, ammonium sulphate, H₃PO₄, Na₃PO₄, K₃PO₄, KNO₃, NaNO₃, C₆–C₁₄ arylsulphonic acid such as p-toluenesulphonic acid monohydrate, sulphamic acid, C₁–C₆ alkylsulphonic acid such as methylsulphonic acid and ethylsulphonic acid or acetic acid or mixtures thereof in a concentration of from 0.01M to 15M, 0.01M to 10M or 0.25M to 10M, more typically 1M to 10M, even more typically 2 to 9M, yet even more typically 3 to 8M, yet even more typically 4 to 7M, and yet even more typically 5 to 8M. It is especially preferred to use H₂SO₄ in a concentration of from 0.25M to 10M, more typically 1M to 10M, even more typically 2 to 9M, yet even more typically 3 to 8M, yet even more typically 4 to 7M, and yet even more typically 5 to 8M.

The processes of the invention are typically performed in the temperature range 1–99° C., or 5–60° C. more typically 15–40° C.

During the processes of the invention the electrolyte solution is typically stirred or agitated preferably with a mechanical stirrer or by fluidization of the solid reactants using electrolyte solution flow.

The processes of the invention are typically, but not necessarily, conducted under an inert atmosphere such as nitrogen, argon, helium or neon or mixtures thereof.

The positive and negative electrodes can be any shape desired. It is preferred that the positive and negative electrodes are rectangular-plate shaped although the positive electrode can be an expanded metal sheet to allow for zero gap from the membrane while facilitating escape of O₂ gas.

The positive and negative electrodes and the cell design are the same as those described for the HED vanadium electrolyte.

By the processes of the invention stabilized electrolyte solution having vanadium ions in sufficient concentration in an aqueous electrolyte, above saturated concentrations, or 0.1 to 15M or 0.25M to 10M, typically 1M to 10M, and more typically 1.5M to 8M which are suitable for use in a practical all-vanadium battery can be prepared in a single step process. Typically a stabilized aqueous electrolyte having vanadium ions 0.01M to 10M or 0.25M to 10M, more typically 1M to 10M, even more typically 2 to 9M, yet even more typically 3 to 8M, yet even more typically 4 to 7M, and yet even more typically 5 to 8M or 5 to 6M or 5 to 7M or 4 to 5M or 3 to 4M or 2 to 3M or 2 to 3.5M or 3.5 to 5.5M or 4.5 to 5.5M or 3.5 to 4.5M or 2.5 to 3.5M or 2.75 to 3.75M or 3.75 to 4.75M or 4.75 to 5.75M or 5.75 to 6.75M or 7.5 to 7.5M or 6.5 to 7.5M or 5 to 5.5M or 5.5 to 6.5M or 5.001 to 10M or 5.001 to 5.5M, or 5.001 to 6M or 5.001 to 6.5M or 5.001 to 7M or 5.001 to 8M or 5.001 to 9M, for example, vanadium ions (including V(II), V(III), V(IV), and V(V) ions) may be prepared. It is especially preferred to use H₂SO₄ in a concentration of from 0.25M to 10M, more typically 1M to 10M, even more typically 2 to 9M, yet even more typically 3 to 8M, yet even more typically 4 to 7M, and yet even more typically 5 to 8M. By passage of the appropiate number of coulombs an electrolyte solution consisting of 50% M V(III) to 50% M V(IV) can be obtained. Equal volumes of this solution can then be used for each ½-cell so that no overcharge of the positive side is required for the initial charging process.

If precipitation of the V(V) does eventually occur however, it can easily be redissolved and reduced by combining the V(II)/V(III) catholyte with the anolyte containing suspension and/or adding an additional stabilising amount of stabilising agent. This will result in a solution which is mixture of V(III) and V(IV) as in an uncharged battery which can readily be recharged and return the battery to its original state. Occasional mixing of the catholyte and anolyte is beneficial as it assists in rebalancing the cell. Unequal rates of diffusion of the different ions of vanadium across a membrane gradually leads to a greater concentration of vanadium ions on one side, but by periodically mixing the catholyte and anolyte and equally dividing the volumes into the +ve and −ve tanks, a rebalanced cell can be readily achieved. Alternatively any precipitate formed in the battery can be redissolved by reversing the polarity of the cell or stack (or battery) and slowly recharging the electrolyte solutions.

A further embodiment of the invention involves an electrochemical apparatus for power delivery employing an array of cells comprising a positive electrode at one end of the array, a negative electrode at the other end of the array, and one or more bipolar electrodes between the end electrodes. A solution of hydrogen peroxide or a bubbly dispersion of air/oxygen in an electrolyte solution is pumped through the positive ½-cells of the array while a stabilized solution of V(II) or V(II)/V(III) is pumped through the negative ½-cells to produce energy (and thus electricity) according to the reactions:

Positive electrode: H₂O₂+2H⁺+2e→2H₂O or

-   -   ½O₂+2H⁺+2e→H₂O

Negative electrode: ½V²⁺→2V³⁺+2e

DESCRIPTION OF DRAWINGS

Preferred embodiments of the invention are described below with reference to the following drawings in which:

FIG. 1 depicts schematically an electrochemical cell having an ionically conducting separator for dissolving and reducing a reducible vanadium-containing salt or complex, optionally in the presence of a stabilising agent;

FIG. 2 depicts schematically a batch process for dissolving and reducing a reducible vanadium-containing salt or complex, optionally in the presence of a stabilising agent;

FIG. 3 depicts schematically a continuous process for dissolving and reducing a reducible vanadium-containing salt or complex, optionally in the presence of a stabilising agent;

FIG. 4 depicts schematically an electrochemical cell which does not have an ionically conducting separator for dissolving and reducing a reducible vanadium compound, optionally in the presence of a stabilising agent, the electrolyte solution produced comprising typically a mixture of V(IV) and V(V) ions in the electrolyte solution;

FIG. 5 depicts schematically an apparatus for dissolving and reducing a reducible vanadium compound, optionally in the presence of a stabilising agent;

FIG. 6 depicts schematically an electrochemical cell which does not have an ionically conducting separator for dissolving and reducing a reducible vanadium compound, the electrolyte solution produced comprising typically a mixture of V(IV) and V(V) ions in the electrolyte solution;

FIG. 7 depicts schematically an electrochemical cell having an ionically conducting separator for dissolving and reducing a reducible vanadium compound;

FIG. 8( a) depicts schematically an alternative process using an electrochemical cell having an ionically conducting separator for generating V(II) or V(III) ions by reducing a mixture of V(IV) and V(III) and V₂O₅, and a mixing tank for dissolving V₂O₅ or other vanadium salt using the V(II) and/or V(III) ions as reducing agent;

FIG. 8( b) depicts schematically an alternative process using an electrochemical cell having an ionically conducting separator for generating V(V) ions by oxidising a mixture of V(III)/V(IV) and a mixing tank for dissolving V₂O₃ or other vanadium V(II) or V(III) salt using the V(V) as oxidising agent;

FIG. 9 are discharge curves as a function of time at various current densities for an all-vanadium redox battery; employing 5.5M vanadium sulphate in 3M H₂SO₄ and operating at 40° C.;

FIG. 10 depicts an all-vanadium redox battery system;

FIG. 11 depicts an all-vanadium redox battery fuel cell system;

FIG. 12 depicts schematically an electrochemical cell having an ionically conducting separator for dissolving and reducing a reducible vanadium-containing salt or complex in the presence of a stabilising agent;

FIG. 13 depicts an all-vanadium redox battery system;

FIG. 14 depicts effect of sulphuric acid concentration on V(II) sulphate solubility;

FIG. 15 depicts effect of sulphuric acid concentration on V(III) sulphate solubility;

FIG. 16 depicts effect of sulphuric acid concentration on vanadyl sulphate solubility; and

FIG. 17 depicts schematically an electrochemical cell having an ionically conducting separator for dissolving and reducing a reducible vanadium compound in the presence of a stabilising agent.

BEST MODE AND OTHER MODES OF CARRYING OUT THE INVENTION

Referring to FIG. 1 an electrochemical cell 20 for dissolving and reducing a reducible vanadium-containing salt or complex has a positive compartment 24 containing a catholyte 25 in electrical contact with positive electrode 26. Cell 20 has a negative compartment 21 containing an anolyte 22 in electrical contact with negative electrode 23. Positive electrode 26 is electrically coupled to a negative electrode 23 via electrical power source 204 and switch 205 which are connected in series. Power source 204 can be a dc battery capable of delivering of at least about 2.3 volts over and above resistant losses of cell 20. Ionically conducting separator 27 is disposed between positive and negative compartments 24 and 21 and is in contact with catholyte 25 and anolyte 22 to provide ionic communication therebetween. A preferred separator 27 is a Selemion or New Selemion or Flemion or Nafion membrane. Catholyte 25 is typically 1M to 12M H₂SO₄. Anolyte 22 is typically 1M to 12M H₂SO₄ and contains a reducible vanadium-containing salt or complex such as V₂O₅ in powder form and optionally a stabilising amount of stabilising agent.

To dissolve and reduce the powdered V₂O₅, anolyte 22 is stirred by teflon coated magnetic stirrer bar 28 which is driven by magnetic stirrer/hot plate 29 disposed below negative compartment 21. Nitrogen is bubbled through anolyte 22 via line 201 which delivers nitrogen from nitrogen gas cylinder 202 to which it is coupled. Nitrogen is vented from negative compartment 21 via vent 203. The temperature of the solution may be at room temperature but is typically maintained in an elevated temperature range above room temperature from 25 to 70° C., typically 35–50° C., during the dissolution process (typically by using hot plate 29). Switch 205 is closed so as to deliver 2.5 volts between negative and positive electrodes 23 and 26. The following reactions take place at negative electrode 23 or in positive compartment 21 as a consequence of reaction of ions formed by reactions which take place at negative electrode 23:

(a) V(V)+3e⁻→V(II)

(b) V(V)+2e⁻→V(III)

(c) V(V)+e⁻→V(IV)

(d) (i) V(II)+V(IV)→2V(III)

-   -   (ii) V(II)+½V₂O₅→V(III)/V(IV)     -   (iii) V(III)+½V₂O₅→2V(IV)     -   (iv) V(IV)+½V₂O₅→V(V) (in solution)+V(IV)

From the above reactions the V(II), V(III) and V(IV) ions dissolved in anolyte 22 reduce the V₂O₅ powder and overall are reduced to the extent of forming dissolved V(III) and V(IV) ions. Powdered V₂O₅ which comes in direct contact with negative electrode 23 is directly reduced and at the positive electrode 26, water is decomposed producing O₂.

Enough powdered V₂O₅ is used to form a HED solution. Initially a viscous HED solution is formed (which may be a colloidal particle/solution mixture) of vanadium ions (typically >1.8M vanadium ions, typically 3.01M–10M, more typically 5.01M–6.5M). The viscous HED solution is then typically maintained, with or without stirring, at room temperature for about 3 weeks to a month or more, or at 25–99° C., more typically 25–95° C. or 35–99° C., for 0.1 day–30 days, typically 0.5 day–20 days, until its viscosity substantially decreases. The V(II), V(III) and V(IV) ions in the HED solution, before or after reducing the viscosity of the HED solution, may be reduced to form a solution of V(II)/V(III) ions or oxidised to form a solution of V(IV)/V(V) ions. A stabilising amount of a stabilising agent may be optionally added.

An example of a batch process for preparing a HED all-vanadium electrolyte solution for a charged all vanadium redox battery containing using the process of the invention is depicted in FIG. 2.

FIG. 3 depicts an example of a continuous process for preparing a HED all-vanadium electrolyte solution for a charged all vanadium redox battery using the process of the invention.

Referring to FIG. 4 an electrochemical cell 10 for dissolving and reducing a reducible vanadium compound has a negative electrode 11 and a positive electrode 12 which are electrically coupled via electrical power source 13 and switch 14 which are connected in series. Power source 13 can be a dc battery capable of delivering at least about 0.5 to about 2.0 volts over and above resistance losses of cell 10. Cell 10 contains an aqueous electrolyte which is in electrical contact with positive and negative electrodes 12 and 11. Electrolyte solution 15 is preferably 0.5M to 12M H₂SO₄ and contains 3.01M to 10M, more typically 4–8M vanadium from a reducible vanadium compound such as V₂O₅ or ammonium metavanadate in powder form and optionally a stabilising amount of stabilising agent.

To dissolve and reduce the powdered V₂O₅ electrolyte solution 15 is stirred by teflon coated stirrer bar 16 which is driven by magnetic stirrer/hot plate 17 disposed below cell 10. Nitrogen is bubbled through electrolyte solution 15 via line 18 which delivers nitrogen from nitrogen gas cylinder 19 to which it is coupled. Nitrogen is vented from cell 10 via vent 101. The temperature of the solution may be at room temperature but is typically maintained in an elevated temperature range above room temperature from 25 to 70° C., typically 35–50° C., during the dissolution process (typically by using hot plate 17). Switch 14 is closed so as to deliver 0.5 to 2.0 volts between negative and positive electrodes 11 and 12. Initially a viscous HED solution is formed (which may be a colloidal particle/solution mixture) of vanadium ions (typically >3M vanadium ions, typically 3.01M–10M, more typically 5.01M–6.5M). The viscous HED solution is then typically maintained, with or without stirring, at room temperature for about 3 weeks to a month or more, or at 25–99° C., more typically 25–80° C. for 0.1 day–25 days, typically 1 day–15 days, until its viscosity substantially decreases. The V(II), V(III) and V(IV) ions in the HED solution, before or after reducing the viscosity of the HED solution, may be reduced to form a solution of V(II)/V(III) ions or oxidised to form a solution of V(IV)/V(V) ions. An effective amount of a stabilising agent may be added to the reduced and/or oxidised solution to stabilise the solution(s) if required.

Referring to FIG. 5 a container 30 for dissolving and reducing ammonium metavanadate or vanadium pentoxide or other reducible vanadium salts or complexes is disposed on top of magnetic stirrer 31. For exemplification a process of dissolving and reducing ammonium vanadate is described. Container 30 contains an aqueous electrolyte solution 32 comprising 0.5M to 12M H₂SO₄ and ammonium vanadate in powder form and optionally a stabilising amount of a stabilising agent (typically 0.75–5 wt %) such as glycerine, inositol or sodium gluconate.

To dissolve 1.801M to 10M, typically 3.01M to 10M of the powdered ammonium vanadate electrolyte solution 32 is stirred by teflon coated stirrer bar 33 which is driven by magnetic stirrer/hot plate 31. Nitrogen is bubbled through electrolyte solution 32 via line 34 which delivers nitrogen from nitrogen gas cylinder 35 to which it is coupled. Nitrogen is vented from container 30 via vent 36. The temperature of the solution may be at room temperature but is typically maintained in an elevated temperature range above room temperature from 25 to 70° C., typically 35–50° C., during the dissolution process (typically by using hot plate 31). A chemical reductant preferably SO₂, H₂O₂, or oxalic acid (0.05M to 10M) is added to electrolyte solution 32 from reservoir 37 by opening tap 39. Sufficient reductant is added to dissolve and reduce the ammonium vanadate powder in electrolyte solution 32, optionally in the presence of a stabilising amount of a suitable stabilising agent, to initially form a viscous HED solution (which may be a colloidal particle/solution mixture) of vanadium ions (>1.8M vanadium ions, typically 1.801–10M, more typically 2.01–10M, even more typically 3.01M–10M, more typically 4.01M–6.5M, more typically 5.01M–6.5M). The viscous HED solution is then typically maintained, with or without stirring, at 25–99° C., more typically 25–75° C. for 0.1 day–25 days, typically 1 day–15 days, until its viscosity substantially decreases. The V(II), V(III) and V(IV) ions in the HED solution, before or after reducing the viscosity of the HED solution, may be reduced to form a solution of V(II)/V(III) ions or oxidised to form a solution of V(IV)/V(V) ions.

Referring to FIG. 6 an electrochemical cell 40 for dissolving and reducing a reducible vanadium compound is the same as electrochemical cell 10 shown in FIG. 4 except it includes a reservoir 41 which contains a chemical reductant preferably SO₂ or oxalic acid (0.05M to 10M, more typically 0.1 to 1M). The temperature of the solution may be at room temperature but is typically maintained in an elevated temperature range above room temperature from 25 to 99° C., typically 25 to 70° C., more typically 35–50° C., during the dissolution process (typically by using a hot plate). Electrochemical cell 40 can be used to dissolve and reduce a reducible vanadium compound such as 3.01M to 10M (or more) V₂O₅ in the same way as electrochemical cell 10 in FIG. 4 is used except the chemical reductant is added to electrolyte solution 42 from reservoir 41 by opening tap 43. Sufficient reductant is added to assist in dissolving and reducing the V₂O₅ powder which is in electrolyte solution 42 prior to further reduction. A stabilising amount of a suitable stabilising agent may be optionally added.

The following reactions take place at negative electrode 11 or as a consequence of reactions of ions formed by reactions which take place at negative electrode 11:

(a) V⁵⁺+3e⁻→V²⁺

(b) V⁵⁺+2e⁻→V³⁺

(c) V⁵⁺+e⁻→V⁴⁺

(d) (i) V²⁺+V⁴⁺→2V³⁺

-   -   (ii) V²⁺+½V₂O₅→V³⁺/V⁴⁺     -   (iii) V³⁺+½V₂O₅→2V⁴⁺     -   (iv) V⁴⁺+½V₂O₅→V⁵⁺ (in solution)+V⁴⁺

From the above reactions the V(II), V(III) and V(IV) ions dissolved in electrolyte solution 15 reduce the V₂O₅ powder and form dissolved and reduced V(II), V(III), V(IV) and V(V) ions. Powdered V₂O₅ which comes into contact with negative electrode 11 is also reduced. At positive electrode 12 the following reactions take place:

-   -   (a) V²⁺→V³⁺, V⁴⁺ or V⁵⁺ (in solution)+1, 2 or 3e⁻     -   (b) V³⁺→V⁴⁺ or V⁵⁺ (in solution)+1 or 2e⁻     -   (c) V⁴⁺→V⁵⁺ (in solution)+1e⁻     -   (d) H₂O→O₂

From the immediately preceding reactions whilst V(II), V(III) and V(IV) ions are oxidised to higher oxidation states at positive electrode 12 the higher oxidation state vanadium ions thus formed remain in solution. Initially a viscous HED solution is formed (which may be a colloidal particle/solution mixture) of vanadium ions (>1.8M vanadium ions, typically >2M vanadium ions, even more typically >3M vanadium ions, typically 3.01M–10M, more typically 5.01M–6.5M). The viscous HED solution is then typically maintained, with or without stirring, at room temperature for about 3 weeks to a month or more, or at 25–99° C., typically 25–80° C. for 0.1 day–25 days, typically 1 day–15 days, until its viscosity substantially decreases. The V(II), V(III) and V(IV) ions in the HED solution, before or after reducing the viscosity of the HED solution, may be reduced to form a solution of V(II)/V(III) ions or oxidised to form a solution of V(IV)/V(V) ions. Referring to FIG. 7 an electrochemical cell 50 for dissolving and reducing a reducible vanadium compound is the same as electrolyte solution chemical cell 20 in FIG. 1 except it has a reservoir 51 which contains a chemical reductant preferably oxalic acid (0.05M to 5M). Electrochemical cell 50 can be used to dissolve and reduce 3–10M, for example, of a reducible vanadium compound such as V₂O₅ in the same way as electrochemical cell 20 in FIG. 1 is used except the chemical reductant is added to electrolyte solution 52 from reservoir 51 by opening tap 53. Sufficient reductant is added to assist in dissolving and reducing the V₂O₅ powder which is in electrolyte solution 52. A stabilising amount of a suitable stabilising agent is optionally added. The temperature of the solution may be at room temperature but is typically maintained in an elevated temperature range above room temperature from 25 to 99° C., typically 25 to 70° C., more typically 35–99° C., yet more typically 35 to 50° C., during the dissolution process (typically by using magnetic stirrer/hot plate 54). Initially a viscous HED solution is formed (which may be a colloidal particle/solution mixture) of vanadium ions (>1.8M vanadium ions, typically >2M vanadium ions, even more typically >3M vanadium ions, typically 3.01M–10M, more typically 5.01M–6.5M). The viscous HED solution is then typically maintained, with or without stirring, at room temperature for about 3 weeks to a month or more, or at 25–99° C., typically 25–80° C. for 0.1 day–25 days, typically 1 day–15 days, until its viscosity substantially decreases. The V(II), V(III) and V(IV) ions in the HED solution, before or after reducing the viscosity of the HED solution, may be reduced to form a solution of V(II)/V(III) ions or oxidised to form a solution of V(IV)/V(V) ions.

FIG. 8( a) depicts a batch or continuous process for preparing HED electrolyte solutions respectively. In FIG. 8( a) 1.801M–10M, typically 2–5M, V₂O₅ powder (or NH₄VO₃ powder), and H₂SO₄, and optionally a stabilising amount of a stabilising agent, are fed into a mixing tank and a solution of V(III) is added continuously as a leachant/reductant for the V₂O₅. The V(III) reduces the V₂O₅ to V(IV) producing a solution containing a 50:50 mixture of V(III) and V(IV) ions at supersaturation levels. Part of this electrolyte solution is recycled to the negative compartment of an electrolytic cell where it is reduced to V(III) and returned to the mixing tank for further leaching of V₂O₅. The remaining V(III)/V(IV) electrolyte solution is used as feed for the positive and negative ½-cells of a vanadium redox cell which upon charging, produces electrolyte solutions of V(II)/V(III) and V(IV)/V(V) in the negative and positive ½-cells respectively. Initially a viscous HED solution is formed (which may be a colloidal particle/solution mixture) of vanadium ions (>1.8M vanadium ions, typically >2M vanadium ions, even more typically >3M vanadium ions, typically 3.01M–10M, more typically 5.01M–6.5M). The viscous HED solution is then typically maintained, with or without stirring, at room temperature for about 3 weeks to a month or more, or at 25–99° C., typically 25–80° C. for 0.1 day–25 days, typically 1 day–15 days, until its viscosity substantially decreases. The V(II), V(III) and V(IV) ions in the HED solution, before or after reducing the viscosity of the HED solution, may be reduced to form a solution of V(II)/V(III) ions or oxidised to form a solution of V(V)/V(V) ions.

FIG. 8( b) depicts schematically an alternative batch or continuous process for preparing HED electrolyte solutions, wherein 1.801M–10M, typically 2–5M, V₂O₃ and/or V₂O₄ and/or VOSO₄ powder, H₂SO₄ and optionally a stabilising amount of a stabilising agent, are fed into a mixing tank and a solution of V(V) is added continuously as an oxidising agent for the V₂O₃, and/or V₂O₄ and/or VOSO₄. The V(V) oxidises the V₂O₃, and/or V₂O₄ and/or VOSO₄ to V(IV) producing a solution of V(IV)/V(V) ions at up to and including supersaturation levels. Part of this electrolyte solution is recycled to the positive compartment of an electrolytic cell where it is oxidised to V(V) and returned to the mixing tank for further oxidation of V₂O₃ and/or V₂O₄ and/or VOSO₄. The V(IV)/V(V) electrolyte solution is used as feed for the positive ½-cell of a vanadium redox cell which, upon charging, produces electrolyte solutions of V(II)/V(III) and V(IV)/V(V) in the negative and positive ½-cells respectively. Initially a viscous HED solution is formed (which may be a colloidal particle/solution mixture) of vanadium ions (>1.8M vanadium ions, typically >2M vanadium ions, even more typically >3M vanadium ions, typically 3.01M–10M, more typically 5.01M–6.5M). The viscous HED solution is then typically maintained, with or without stirring, at room temperature for about 3 weeks to a month or more, or at 25–99° C., typically 25–80° C. for 0.1 day–25 days, typically 1 day–15 days, until its viscosity substantially decreases. The V(II), V(III) and V(IV) ions in the HED solution, before or after reducing the viscosity of the HED solution, may be reduced to form a solution of V(II)/V(III) ions or oxidised to form a solution of V(IV)/V(V) ions.

FIG. 9 shows discharge curves for a vanadium redox cell employing 5.5M vanadium electrolyte solutions at 2 current densities.

FIG. 10 schematically depicts an all-vanadium redox battery system 900. System 900 includes an all-vanadium redox battery 901 having a negative compartment 902 which includes an anolyte 902 a therein in electrical contact with a negative electrode 903 and a positive compartment 904 which includes a catholyte 904 a therein in electrical contact with a positive electrode 905. An ionically conducting separator 906 is disposed between negative and positive compartments 902 and 904 and is in contact with anolyte 902 a and catholyte 904 a to provide ionic communication therebetween. Anolyte 902 a and catholyte 904 a are typically prepared by a method in which a HED solution of a soluble vanadium salt such as V₂O₅ or ammonium vanadate is electrolytically reduced in an aqueous solution of concentrated sulphuric acid (1–12M) to a 100% V³⁺ oxidation state. V₂O₅ powder is then added to the V³⁺ solution and is induced to dissolve in the V³⁺ solution by the V³⁺ ions which act as a leaching agent for the V₂O₅. This solution is then placed in an electrolysis cell and reduced to V^(3.5+). Additional V₂O₅ powder (in an amount to produce a final supersaturated solution, typically 3.01–10M vanadium ions) is added to V^(3.5+) solution and mixed by mechanical stirring and after the dissolution reaction is completed the solution is filtered. The vanadium oxidation state of the solution obtained is typically close to 100% V⁴⁺. The supersaturated (e.g. 5–10M) V(IV) electrolyte solution is then placed into anolyte reservoir 907 and negative compartment 902 and catholyte reservoir 908 and positive compartment 904. Thin air sealing layers 930 a, 930 b, 930 c and 930 d of paraffin oil are placed in negative and positive compartments 902 and 904 and into anolyte reservoir 907 and catholyte reservoir 908 to substantially seal anolyte 902 a and catholyte 904 a from air. Initially anolyte 902 a and catholyte 904 a are viscous HED solutions (which may be a colloidal particle/solution mixtures) of vanadium ions (>1.8M vanadium ions, typically >2M vanadium ions, even more typically >3M vanadium ions, typically 3.01M–10M, more typically 5.01M–6.5M). The viscous HED solution may be maintained, with or without stirring, e.g. by pumping, at room temperature for about 3 weeks to a month or more, or at 25–99° C., typically 25–80° C. for 0.1 day–25 days, typically 1 day–15 days, until the viscosity substantially decreases. Anolyte 902 a is pumped through negative compartment 902 and anolyte reservoir 907 via anolyte supply and return lines 909 and 910 by anolyte pumps 911 and 911 a, and at the same time catholyte 904 a is pumped through positive compartment 904 and catholyte reservoir 908 via catholyte supply and return lines 912 and 913 by catholyte pumps 914 and 914 a. Redox battery 901 is charged by providing electrical energy from power source 915 to positive and negative electrodes 903 and 905 by closing switch 916 and opening switch 917 whereby electricity flows in negative and positive electrodes 903 and 905 from power supply 915 to produce a supersaturated concentration of divalent vanadium ions in anolyte 902 a and a supersaturated concentration of pentavalent vanadium ions in catholyte 904 a. Redox battery 911 may be insulated so as to substantially prevent or significantly reduce crystallisation or precipitation of vanadium substances/compounds from the catholyte and/or anolyte, i.e. so the temperature of the operating redox battery 901 is maintained typically above 20° C. (unless a stabilising agent is used in which case depending on the stabilising agent it may be possible to operate above 0° C.), more typically above 25° C., typically in the range 25° C.–50° C. via heating and/or cooling jacket 940 having inlet 941 and outlet 942. Inlets 941, 944 and 947 are coupled to pumps 951, 953 and 952 via lines 962, 963 and 964. Computer 960 is coupled to pumps 951, 953 and 952 via lines 965, 966 and 967 to control the speed of such pumps and to reservoirs 968 and 969 via lines 970 and 971 to control the outputs of such reservoirs. Reservoirs 968 and 969 are coupled to reservoirs 904 a and 902 a via lines 970 and 971. Computer 960 is linked to probes 972 and 973 via lines 974 and 975 and to probes 976 and 977 via lines 978 and 979. Computer 960 may be linked to pumps 914 a, 911 a, 914 and 911 to control the speed of such pumps. Probes 972, 973, 976 and 977 may be simply probes for measuring temperature or may each consist of a plurality of probes which measure desired parameters (e.g. temperature, pH, electrolyte concentration, total sulphate concentration, vanadium ion concentration, vanadium redox couple concentration, stabilising agent concentration, flow rate, and/or oxygen concentration). Once a particular parameter is detected by one or more of probes 972, 973, 976 and 977 a signal is sent via the appropriate line to computer 960 which in turn sends a signal, if required to the appropriate entity (e.g. one of pumps 951, 952 or 953 or to supply 950 or to reservoir 968 or 969) to take the appropriate action. For instance, the temperature of anolyte 902 a in anolyte reservoir 907 is maintained and/or controlled typically above 20° C. (unless a stabilising agent is used in which case depending on the stabilising agent it may be possible to operate above 0° C.), more typically above 25° C., typically in the range 25° C.–50° C. via heating and/or cooling jacket 943 having inlet 944 and outlet 945 (steam, hot water, cold water or water at an appropriate temperature may be passed at an appropriate rate through jacket 943 under the control of computer 960 to maintain and/or control the temperature of anolyte 902 a in reservoir 907). The temperature of catholyte 904 a in catholyte reservoir 908 is maintained and/or controlled typically above 20° C. (unless a stabilising agent is used in which case depending on the stabilising agent it may be possible to operate above 0° C.), more typically above 25° C., typically in the range 25° C.–50° C. via heating and/or cooling jacket 946 having inlet 947 and outlet 948 (steam, hot water, cold water or water at an appropriate temperature may be passed at an appropriate rate through jacket 946 under the control of computer 960 to maintain and/or control the temperature of catholyte 904 a in reservoir 908). Steam, hot water, cold water or water at an appropriate temperature may be passed at an appropriate rate through jacket 940 under the control of computer 960 to maintain the temperature at the desired temperature or within the desired temperature range of anolyte 902 a and catholyte 904 a in battery 901 via steam, hot water, cold water or water supply 950 which is coupled to pumps 951, 952 and 953 via lines 954, 955 and 956, to outlets 942, 945 and 948 via lines 957, 958 and 959 and to computer 960 via line 961. The temperatures of anolyte 902 a and catholyte 904 a may be manually or automatically monitored using a thermometer or thermostat or other appropriate temperature sensing device and the temperature of anolyte 902 a and catholyte 904 a controlled or maintained manually or automatically by adjusting the flow rate of steam, hot water, cold water or water at an appropriate temperature through the appropriate heating jacket(s) 940, 943 and/or 946. Alternatively, a wider operating temperature may be achieved by the use of a suitable stabilising agent in anolyte 902 a and catholyte 904 a. Reservoirs 968 and 969 may contain stabilising agent and/or electrolyte which can be added to reservoirs 904 a and 902 a as appropriate under the control of computer 960.

Electricity is derived from redox battery 911 by opening switch 916, closing switch 917 and withdrawing electrical energy via load 918 which is in electrical communication with negative and positive electrodes 903 and 905.

Redox battery 901 is recharged by opening switch 917, closing switch 916 and providing electrical energy from power source 915 to derive a supersaturated solution of divalent ions in anolyte 902 a and a supersaturated solution of pentavalent ions in catholyte 904 a. The anolyte 902 a and catholyte 904 a may be rebalanced 904 a prior to, during or after the recharging process, to take into account any cross-contamination between anolyte 902 a and catholyte 904 a.

FIG. 11 schematically depicts an all-vanadium redox battery/fuel cell system 1000. System 1000 includes an all-vanadium redox battery/fuel cell 1001 having a negative compartment 1002 which includes an anolyte 1002 a therein in electrical contact with a negative electrode 1003 and a positive compartment 1004 which includes a catholyte 1004 a therein in electrical contact with a positive oxygen/air electrode 1005. An ionically conducting separator 1006 is disposed between negative and positive compartments 1002 and 1004 and is in contact with anolyte 1002 a and catholyte 1004 a to provide ionic communication therebetween. Anolyte 1002 a and catholyte 1004 a are typically prepared by a method in which a solution of a vanadium compound such as V₂O₅ powder is electrolytically reduced, optionally in the presence of a stabilising amount of a suitable stabilising agent, in an aqueous solution of concentrated sulphuric acid (1–10M) to a 100% V³⁺ oxidation state. V₂O₅ powder is then added to the V³⁺ solution and is induced to dissolve in the V³⁺ solution by the V³⁺ ions which act as a leaching agent for the V₂O₅. This solution is then placed in an electrolysis cell and reduced to V^(3.5+). Additional V₂O₅ powder (in an amount to produce a final supersaturated solution) is added to V^(3.5+) solution and mixed by mechanical stirring and after the dissolution reaction is completed the solution is filtered. The vanadium oxidation state of the solution obtained is typically close to 100% V⁴⁺. The solution obtained is supersaturated (e.g. 5–10M) Part of the V(IV) electrolyte solution is then reduced to V(II) in a separate anolyte charging cell (not shown) and placed into anolyte reservoir 1007 and negative compartment 1002. Part of the V(IV) electrolyte solution may be optionally oxidised to V(V) in a separate catholyte charging cell (not shown) and placed in positive compartment 1004. Thin air sealing layers 1030 a, 1030 b, and 1030 c of paraffin oil are placed in negative and positive compartments 1002 and 1004 and into anolyte reservoir 1007 to substantially seal anolyte 1002 a and catholyte 1004 a from air. Anolyte 1002 a is pumped through negative compartment 1002 and anolyte reservoir 1007 via anolyte supply and return lines 1009 and 1010 by anolyte pumps 1011 and 1011 a, and at the same time oxygen or an oxygen containing gas such as air, is passed through compartment 1004 b via inlet line 1004 c and water exits compartment 1004 b via exit line 1004 d. Catholyte 1004 a is charged by passing oxygen or an oxygen containing gas over oxygen/air electrode 1005 (eg a porous carbon oxygen electrode) to oxidise vanadium (IV) to vanadium(V) in catholyte 1004 a. Anolyte 1002 a may be charged in a separate charging cell (as may catholyte 1004 a when all of anolyte 1002 a is discharged to rebalance system 1000). Initially catholyte 1004 a and anolyte 1002 a are viscous HED solutions (which may be a colloidal particle/solution mixture) of vanadium ions (typically >3M vanadium ions, typically 3.01M–10M, more typically 5.01M–6.5M). The viscous HED solutions are then optionally maintained, with or without stirring, e.g. by pumping, at room temperature for about 3 weeks to a month or more, or at 25–99° C., typically 25–80° C. for 0.1 day–25 days, typically 1 day–15 days, until their viscosities substantially decrease. Electricity is derived from redox battery 1001 by closing switch 1017 and withdrawing electrical energy via load 1018 which is in electrical communication with negative and positive electrodes 1003 and 1005. Since catholyte 1004 a is instantaneously regenerated by oxygen via oxygen/air electrode 1005, a catholyte reservoir is not required, thus permitting, for a given size battery, twice the volume of the anolyte to be carried on a vehicle such as a car and thereby doubling the range before refuelling. System 1000 has a theoretical energy density of 270.7 Wh/kg.

The anolyte 1002 a and catholyte 1004 a may be rebalanced 1004 a prior to, during or after the recharging process, to take into account any cross-contamination between anolyte 1002 a and catholyte 1004 a.

Referring to FIG. 12 an electrochemical cell 20 for dissolving and reducing a reducible vanadium-containing salt or complex has a positive compartment 24 containing a catholyte 25 in electrical contact with positive electrode 26. Cell 20 has a negative compartment 21 containing an anolyte 22 in electrical contact with positive electrode 23. Positive electrode 26 is electrically coupled to a negative electrode 23 via electrical power source 204 and switch 205 which are connected in series. Power source 204 can be a dc battery capable of delivering of at least about 2.3 volts over and above resistant losses of cell 20. Ionically conducting separator 27 is disposed between positive and negative compartments 24 and 21 and is in contact with catholyte 25 and anolyte 22 to provide ionic communication therebetween. A preferred separator 27 is a Selemion or New Selemion or Flemion or Nafion membrane. Catholyte 25 is typically 1M to 6M H₂SO₄. Anolyte 22 is typically 1M to 6M H₂SO₄ and contains a reducible vanadium-containing salt or complex such as V₂O₅ in powder form. Anolyte 22 optionally contains a stabilising agent used in an amount typically in the range of from 0.1 to 20 wt %, more typically 0.25% to 7.5 wt % (or vol %). Yet more typically, the stabilising agent is used in an amount of from 1% to 3 wt % or 1.5 to 5 wt %.

To dissolve and reduce the powdered V₂O₅, anolyte 22 is stirred by teflon coated magnetic stirrer bar 28 which is driven by magnetic stirrer 29 disposed below negative compartment 21. Nitrogen is bubbled through anolyte 22 via line 201 which delivers nitrogen from nitrogen gas cylinder 202 to which it is coupled. Nitrogen is vented from negative compartment 21 via vent 203. Switch 205 is closed so as to deliver 2.5 volts between negative and positive electrodes 23 and 26. The following reactions take place at negative electrode 23 or in positive compartment 21 as a consequence of reaction of ions formed by reactions which take place at negative electrode 23:

(a) V(V)+3e⁻→V(II)

(b) V(V)+2e⁻→V(III)

(c) V(V)+e⁻→V(IV)

(d) (i) V(II)+V(IV)→2V(III)

-   -   (ii) V(II)+½V₂O₅→V(III)/V(IV)     -   (iii) V(III)+½V₂O₅→2V(IV)     -   (iv) V(IV)+½V₂O₅→V(V) (in solution)+V(IV)

From the above reactions the V(II), V(III) and V(IV) ions dissolved in anolyte 22 reduce the V₂O₅ powder and overall are reduced to the extent of forming dissolved V(III) and V(IV) ions. Powdered V₂O₅ which comes in direct contact with negative electrode 23 is directly reduced. Water is decomposed at the positive electrode producing O₂. Overall the reactions in the anolyte can be represented as:

-   -   Reducing Conditions         V₂O₅+stabilising agent→V(III)/V(IV)+stabilising agent

The addition of a stabilising agent as defined above to an aqueous solution of a vanadium salt can have a very substantial effect on the solubility of that salt. Thus, vanadium pentoxide is normally very slightly soluble in water (0.07 g/l). However, with the addition of as little as 0.5–3% by weight of stabilising agent (e.g. glycerine+ammonium oxalate) a 0.5M solution of vanadium ions in water can be prepared. Similarly, a 0.487M solution of vanadium pentoxide may be prepared in 3M H₂SO₄ by boiling and subsequently cooling. When 0.5–3% by weight of stabilising agent is added, a concentration of up to 3.5–5M vanadium ions is achievable (depending on the stabilising agent) by simple dissolution.

In an all vanadium redox cell tested by the inventors which did not include an effective stabilising amount of a stabilising agent, the V(III)/V(IV) electrolyte solution, prepared by the electrolytic dissolution of V₂O₅ powder, had a maximum concentration of vanadium of 2.46M, and is stable at room temperature. With the addition of 0.5–9%, more typically 2–3% by weight of stabilising agent (glycerine+ammonium oxalate based on the weight of vanadium pentoxide) a concentration of up to 4.21M V₂O₅ can be achieved. This solution is stable at room temperature for a period of at least several months. In the event that vanadium salts start precipitating from solution, further additions of stabilising agent can be made to the solution as required.

FIG. 13 schematically depicts an all-vanadium redox battery system 900. System 900 includes an all-vanadium redox battery 901 having a negative compartment 902 which includes an anolyte 902 a therein in electrical contact with a negative electrode 903 and a positive compartment 904 which includes a catholyte 904 a therein in electrical contact with a positive electrode 905. An ionically conducting separator 906 is disposed between negative and positive compartments 902 and 904 and is in contact with anolyte 902 a and catholyte 904 a to provide ionic communication therebetween. Anolyte 902 a and catholyte 904 a are typically prepared by a method in which a solution of a soluble vanadium salt such as ammonium vanadate is electrolytically reduced in an aqueous solution of concentrated sulphuric acid (1–10M) to a 100% V³⁺ oxidation state. V₂O₅ powder and an effective stabilising amount of a stabilising agent (typically 0.5–10% w/w) is then added to the V³⁺ solution and is induced to dissolve in the V³⁺ solution by the V³⁺ ions which act as a leaching agent for the V₂O₅. This solution is then placed in an electrolysis cell and reduced to V^(3.5+). Additional V₂O₅ powder (in an amount to produce a final supersaturated solution) and an effective stabilising amount of a stabilising agent (typically 0.5–10% w/w) is added to V^(3.5+) solution and mixed by mechanical stirring and after the dissolution reaction is completed the solution is filtered. The vanadium oxidation state of the solution obtained is typically close to 100% V⁴⁺. The supersaturated (e.g. 4–10M) V(IV) electrolyte solution is then placed into anolyte reservoir 907 and negative compartment 902 and catholyte reservoir 908 and positive compartment 904. Thin air sealing layers 930 a, 930 b, 930 c and 930 d of paraffin oil are placed in negative and positive compartments 902 and 904 and into anolyte reservoir 907 and catholyte reservoir 908 to substantially seal anolyte 902 a and catholyte 904 a from air. Anolyte 902 a is pumped through negative compartment 902 and anolyte reservoir 907 via anolyte supply and return lines 909 and 910 by anolyte pumps 911 and 911 a, and at the same time catholyte 904 a is pumped through positive compartment 904 and catholyte reservoir 908 via catholyte supply and return lines 912 and 913 by catholyte pumps 914 and 914 a. Redox battery 901 is charged by providing electrical energy from power source 915 to positive and negative electrodes 903 and 905 by closing switch 916 and opening switch 917 whereby electricity flows in negative and positive electrodes 903 and 905 from power supply 915 to produce a supersaturated concentration of divalent vanadium ions in anolyte 902 a and a supersaturated concentration of pentavalent vanadium ions in catholyte 904 a. Electricity is derived from redox battery 911 by opening switch 916, closing switch 917 and withdrawing electrical energy via load 918 which is in electrical communication with negative and positive electrodes 903 and 905.

Redox battery 901 is recharged by opening switch 917, closing switch 916 and providing electrical energy from power source 915 to derive a supersaturated solution of divalent ions in anolyte 902 a and a supersaturated solution of pentavalent ions in catholyte 904 a. Additional stabilising agent may be added to anolyte 902 a and catholyte 904 a prior to, during or after the recharging process, if desired or if necessary. The anolyte 902 a and catholyte 904 a may be rebalanced 904 a prior to, during or after the recharging process, to take into account any cross-contamination between anolyte 902 a and catholyte 904 a.

FIGS. 14, 15 and 16 show the effect of H₂SO₄ concentration and temperature on the solubilities of V(II), V(III) and V(IV) sulphates in the negative and positive ½ cell electrolyte of the vanadium redox cell.

Referring to FIG. 17 an electrochemical cell 20 for dissolving and reducing a reducible vanadium compound has a positive compartment 24 containing a catholyte with a stabilizing agent 25 in electrical contact with positive electrode 26. Cell 20 has a negative compartment 21 containing an anolyte 22 in electrical contact with positive electrode 23. Positive electrode 26 is electrically coupled to a negative electrode 23 via electrical power source 204 and switch 205 which are connected in series. Power source 204 can be a dc battery capable of delivering at least about 2.3 volts over and above resistance losses of cell 20. Ionically conducting separator 27 is disposed between positive and negative compartments 24 and 21 and is in contact with catholyte 25 and anolyte 22 to provide ionic communication therebetween. A preferred separator 27 is a Nafion membrane or New Selmion membrane. Anolyte 22 is preferably 0.5M to 6.0M H₂SO₄ and contains an effective stabilizing amount of a stabilizing agent (typically 0.5–7.5% w/w), such as inositol or glycerine and a reducible vanadium compound such as V₂O₅ in powder form.

To dissolve and reduce the powdered V₂O₅, anolyte 22 is stirred by teflon coated magnetic stirrer bar 28 which is driven by magnetic stirrer 29 disposed between negative compartment 21. Nitrogen is bubbled through anolyte 22 via line 201 which delivers nitrogen from nitrogen gas cylinder 202 to which it is coupled. Nitrogen is vented from negative compartment 21 via vent 203. Switch 205 is closed so as to deliver 2.5 volts between negative and positive electrodes 23 and 26.

The V(II), V(III) and V(IV) ions produced by reduction of the V₂O₅ powder and dissolved in anolyte 22 to reduce the V₂O₅ powder and form dissolved and reduced V(II), V(III) and V(IV) ions. Powdered V₂O₅ which comes in direct contact with negative electrode 23 is directly reduced and at positive electrode 26, water is decomposed producing O₂. The V(II), V(III) and V(IV) ions may be reduced to form a solution of V(II)/V(III) ions or oxidised to form a solution of V(IV)/V(V) ions. An effective amount of immobilizing agent may be added to the reduced or oxidised solution to immobilise the solution if required.

EXAMPLES Example 1

A 5.5M V(V) solution was prepared by electrolytically oxidising 5.5M VOSO₄ in 3M H₂SO₄. This solution was stable for more than 2 weeks at room temperature followed by 8 weeks at 50° C. When the solution was initially prepared it was very thick and viscous. This solution became less viscous however on standing. After about 2 weeks at 50° C., its viscosity was almost as low as that of a 2M V(V) solution. A sample stored at room temperature however, took more than 4 weeks to reach a similar low viscosity.

Example 2

SO₂ may bubbled through a solution of 3 moles per litre V₂O₅ in 9M sulphuric acid produced 6M V(IV).

Substantially all the V₂O₅ powder dissolved and was reduced by the SO₂ initially to form V(IV) ions in solution. By continuing the SO₂ bubbling the V(IV) ions were further reduced. SO₂ bubbling was continued until the potential of the solution reached that of a 50:50 mixture of V(III) and V(IV) (approx. 0.3 V vs S.C.E. for 2M vanadium in 2M H₂SO₄), which is a suitable HED electrolyte solution for use in a practical all-vanadium battery.

Example 3

An electrolyte solution consisting of 50:50 ratio of 6M V(III) and V(IV) in 9M H₂SO₄ may be prepared by electrolyzing a slurry of 3M of V₂O₅ powder in 1 litre 9M H₂SO₄ in a cell as depicted in FIG. 1.

The process is generally carried out with a separator between the anode and cathode. Since a separator is used, the electrolyte solution in contact with the cathode is usually continuously stirred. Cell Voltage≅2.5 Volts. Substantially all the V₂O₅ powder dissolves and is reduced at the cathode to form V(III)/V(IV) ions in solution. The cell temperature was 40° C.

Example 4

As for Example 2, except that SO₂ was bubbled through the electrolyte solution to assist in reduction of V₂O₅ as well as to keep powder in suspension.

Example 5

As for Example 3, except that SO₂ was bubbled through the electrolyte solution to assist in reduction of V₂O₅ as well as to keep powder in suspension.

Example 6

A 6M solution of a V(III)/V(IV) mixture can be prepared by adding 3 moles per litre V₂O₅ to 9M H₂SO₄ in a cell as depicted in FIG. 1 at 40° C. The polarity of the cell is then reversed and the V(III)/V(IV) mixture is oxidised to produce a 6M V(V) solution which was stable at room temperature for 3 weeks. The temperature was then increased to 50° C. and no precipitate was formed even after 8 weeks.

Example 7

A 5M solution of V(III)/V(IV) can be prepared by adding 2.5 moles per litre V₂O₅ to 6M H₂SO₄ and electrolytically dissolving in a cell as depicted in FIG. 1 at 40° C. The polarity of the cell is then reversed and the vanadium is oxidised to produce a 5M V(V) solution which is stable at a temperature of 50° C. for over 8 weeks.

Example 8

The electrolyte solution was prepared by a method in which the V₂O₅ electrolysis process was separated into two different steps. The solution electrolysis step involved the electrolytic reduction of a solution of vanadium ions to a 100% V³⁺ oxidation state. V₂O₅ is induced to dissolve in the V³⁺ solution by the V³⁺ ions which acts as a leaching agent for the V₂O₅.

A 5.1M vanadium solution was prepared by taking 200 ml of 1.87M V³⁺ solution in about 3M sulphuric acid and adding 35 g of V₂O₅ powder. The powder dissolved after about 10 minutes and the resulting solution was 3.3M V(IV) in 5.35M sulphate. This solution was then placed in an electrolysis cell and reduced to V^(3.5+). A 160 ml portion of the V^(3.5+) solution and 48 g of V₂O₅ powder was mixed by mechanical stirring. The dissolution reaction again proceeded quickly (within about 10 min) and after reaction the mixture was taken and filtered. The filtered solution was titrated with 0.2M KMnO₄ and the resulting concentration of vanadium obtained was 5.1M. The oxidation state of the solution obtained was close to 100% V⁴⁺ with a sulphate concentration of 5.35M. The 5.1M V(IV) electrolyte solution was then placed into both the positive and negative compartments of a small redox battery with an ionically conducting separator therebetween and charged up to the V²⁺ and V(V) states in the positive and negative half cells respectively using a current of approximately 10 mA/cm². The battery was discharged at various current densities and the resultant cell voltage vs time curves as shown in FIG. 9.

Example 9

A 7.1M vanadium solution was prepared by taking 400 ml of 1.87M V³⁺ solution in about 3M sulphuric acid and adding 68 g of V₂O₅ powder plus 44 ml of 18M H₂SO₄. The powder was stirred until fully dissolved and the final solution was 3.4M V(IV). From this solution a volume of 350 ml was placed in the negative compartment of an electrolysis cell and reduced to V³⁺. To this solution 120 g of V₂O₅ powder was added to produce a final V(IV) solution. The concentration of the final solution was determined as 7.1M V⁴⁺. This solution was stable at 40° C. for 3 weeks.

Several methods for preparing vanadium electrolyte solutions are described in the present application. These methods can be used directly to prepare the supersaturated solutions of V³⁺/V(IV) ions. Alternatively, a 2M vanadium solution can be prepared by any of these methods. The supersaturated solution can then be prepared by removing the appropriate amount of water by evaporation, pervaporation or by boiling either at atmospheric pressure or under vacuum until the desired vanadium concentration is reached. Such a process would allow stable supersaturated solutions to be prepared for direct application in the vanadium redox cell.

Further concentrations of the vanadium electrolyte solution can also be undertaken, however either by addition or excess V₂O₅ power during electrolytic or chemical reduction, or by further evaporation or boiling, so as to produce a V³⁺/V(IV) vanadium electrolyte solution concentrate in the form of a slurry or gel. Such a slurry or colloidal concentrate would allow huge volume and weight reductions to be achieved, thus allowing transport costs to be dramatically reduced. Before use in the vanadium battery, the electrolyte solution concentrate can readily be reconstituted simply by adding water until the desired concentration is obtained.

Preparation of the electrolyte solution concentrate takes place at elevated temperatures (above 40° C.) at which the V(II), V(III) and/or V(IV) vanadium ions are in solution. Cooling to room temperature will lead to the formation of a colloidal suspension or vanadium sulphate slurry in the supporting electrolyte solution. Typically, the vanadium content would be in the range 5–20 moles per litre of slurry. The electrolyte solution concentration could be readily reconstituted before use in the vanadium redox battery simply by adding water or dilute acid with or without slight heating to aid redissolution.

A 15M vanadium concentrate can be prepared by slowly adding V₂O₅ powder to 15M H₂SO₄ in the negative compartment of an electrolysis cell at 60° C. until all of the V₂O₅ has been dissolved and reduced to a 50:50 mixture of V³⁺ and V(IV) in H₂SO₄. On cooling to room temperature, the concentrate sets to form a colloidal paste but on reheating to 50° C. and adding water or dilute acid, a 5M solution can be prepared for the vanadium redox cell.

Example 10

A 4M V^(3.5+) solution was employed in an all vanadium redox cell using electrodes of Sigri carbon felt bonded onto a conducting plastic substrate and New Selemion (Type 3) membrane. The cell was charged and discharged several times at a current density of 30 mA/cm² at an ambient temperature of 20 to 30° C. without any precipitation in the positive or negative electrolyte solutions. The cell was then left at 50% state-of-charge for 3 days, during which time the solution temperature dropped below 20° C. overnight. When the pumps were switched on again, a solution blockage was noted in the negative ½ cell. The cell polarity was then reversed and the cell recharged at 20 mA/cm² with the pumps off. After a short period, the pumps were switched back on and no blockage was observed on the negative side. The cell was fully charged and further charge-discharge cycling continued for several weeks with no precipitation problems.

Example 11

Studies show that the rate of the thermal precipitation of V(V) to V₂O₅ increases with increasing temperature but decreases with increasing acid concentration in accordance with the following equilibrium:

${{\frac{1}{2}V_{2}O_{5_{(s)}}} + H_{({aq})}^{+}} = {{VO}_{2_{({aq})}}^{+} + {\frac{1}{2}H_{2}O_{(l)}}}$

The equilibrium constant K is given by:

$K = \frac{\left\lbrack {VO}_{2}^{+} \right\rbrack}{\left\lbrack H^{+} \right\rbrack}$ where log K=0.66±0.06 at 25° C. [10].

In an effort to increase the energy density of the vanadium redox flow cell, the thermal precipitation reaction of V(V) ions in H₂SO₄ has been investigated in greater detail in order to establish the optimum acid concentration, temperature range and precipitation kinetics.

While V(V) solutions of concentrations between 1 and 2M were found to exhibit fairly rapid precipitation rates at temperatures above 40° C., surprising results were in fact obtained with more concentrated solutions This example describes the preparation of V(V) solutions of over 5M which show no signs of thermal precipitation even after several months at temperatures as high as 50° C.

Due to the very low solubility of V₂O₅ in H₂SO₄ V(V) solutions of above 0.1M must be prepared indirectly by oxidation from the more soluble lower oxidation states. In the present study, the V(V) solutions were thus prepared by oxidising V₂O₃ or VOSO₄. The VOSO₄ solutions or V₂O₃ were placed in the positive side of a two-compartment electrolysis cell which employed H₂SO₄ of the same concentration as the catholyte. Two lead electrodes were employed and the ½-cells were separated by an ion exchange membrane (Selemion AMV. Asahi Glass Co. Japan). Nitrogen gas was bubbled through the anolyte to maintain good mass transfer during the electrolysis which was carried out at a current density of 10–20 mA/cm2. The oxidation was continued until the blue V(IV) solution was converted to the deep yellow to yellow-brown colour characteristic of V(V) in H₂SO₄.

Samples of each of the V(V) solutions prepared were stored at both room temperature and at 40–50° C. and their appearance monitored regularly to detect the appearance of any precipitate. Where precipitation was observed, samples were removed periodically, filtered and titrated with KMnOa₄ to determine the change in the vanadium concentration.

A number of V(V) solutions of different vanadium concentration were prepared by oxidation of VOSO₄ solutions in sulphuric acid and their compositions are given in Table 1.

To investigate their thermal stability at elevated temperatures, sealed samples of each solution were placed in a water bath at 40° C. and inspected daily so as to observe their appearance and any signs of precipitation. The results are presented in Table 2.

As expected, the solution of 1.5M V(V), showed no precipitation during the 30 day test while increasing the V(V) concentration up to 2.0M resulted in an increased rate of thermal precipitation. Thus a 2M V(V) solution in 3M H₂SO₄ showed the first signs of precipitation after only two days at 40° C. Increasing the acid concentration to 4M however, increased the stability of the solution so that it took 7 days before any precipitate was observed. This is consistent with the equilibrium reaction given by:

${O_{2{({aq})}}^{+} + {\frac{1}{2}H_{2}O_{(l)}}} = {{\frac{1}{2}V_{2}O_{5{(s)}}} + H_{({aq})}^{+}}$

which shows that increasing the hydrogen ion concentration shifts the reaction to the left, thus increasing the stability of the VO²⁺ ion. After 30 days at 40° C. however, all of the solution samples 1–4 showed very heavy precipitation.

A very surprising result was however obtained when the V(V) concentration was increased to 3M and above. Rather than increasing the rate of thermal precipitation, these solutions showed absolutely no sign of precipitation over the 30 day test period.

What was even more surprising however, was the fact that viscosity of the concentrated V(V) solutions decreased dramatically with time. When initially prepared, the 5.4M V(V) solution for example, was extremely viscous and very difficult to pour. After 30 days at the elevated temperature however, the viscosity had decreased to a similar level as that of the more dilute 2M V(V) solution.

To further study this unexpected phenomenon samples of the V(V) solutions were also exposed to the even higher temperature of 50° C. Again, the 2M V(V) solution in 3M H₂SO₄ precipitated after less than 2 days; however the 3M and above V(V) solutions showed no signs of precipitation even after 2 months at 50° C. The temperature of the 5.4M V(V) solution was further increased to 60° C. and again no precipitate was observed. Although this behaviour cannot be explained at this time, it may be possible that a different V(V) species forms at concentrations of 3M and above, which is not subject to the thermal precipitation reaction of VO²⁺.

TABLE 1 Composition of the V(V) solutions prepared. [V(V)] [H₂SO₄] [SO₄] Solution No. (moles/L) (moles/L) (moles/L) 1 1.5 3.6 4.3 2 1.8 3.6 4.5 3 2.0 3.0 4.0 4 2.0 4.0 5.0 5 3.1 4.5 6.0 6 4.4 5.8 7.0 7 5.4 4.3 7.0

TABLE 2 Appearance of the V(V) solutions stored for 30 days at 40° C. Solution [V(V)] Time for initial evidence Appearance of No. (moles/L) of precipitation (days) solution after 30 days 1 1.5 no ppt no ppt 2 1.8 12 days thick ppt 3 2.0 2 days thick ppt 4 2.0 7 days thick ppt 5 3.1 no ppt no ppt 6 4.4 no ppt no ppt 7 5.4 no ppt no ppt

The above results would suggest that a high H₂SO₄ concentration should be employed to stabilize the V(V) solution against thermal precipitation at temperatures above 40° C. in the vanadium redox battery. Unfortunately however, further experiments revealed that the solubilities of the V(II), V(III) and V(IV) ions in fact decrease with increasing acid concentration as illustrated in FIGS. 14 to 16.

In order to avoid precipitation of any of the four vanadium species during charge/discharge cycling of the vanadium battery employing supersaturated vanadium electrolyte solutions above 2 moles, therefore, higher operating temperatures (above 20° C.) combined with medium to high acid concentrations must be chosen. Fortunately, the rate of precipitation of each vanadium ion is relatively slow, so it is possible to operate with supersaturated solutions which should not precipitate in the cell if the battery is regularly charged and discharged.

The rate of precipitation can be further reduced within the operating temperature range by employing a range of stabilizing agents.

Example 12

The different extent of stabilisation is related to the absorption of these additives on the surface of the nuclei, giving rise to electrostatic repulsion which inhibits precipitation by retarding crystal growth. These stabilising agents can either be organic or inorganic. Inorganic additives include ammonium compounds, phosphates and polyphosphates. For example, a diphosphoric acid has the following structure:

which contains —OH and ═O groups which are able to absorb on the surface of the nuclei and inhibit precipitation.

Typical organic compounds contain one or more —OH, ═O, —SH or —NH₂ groups, or combinations of these groups which can also absorb on the surface of the nuclei and inhibit precipitation. Such inorganic and organic compounds (containing one or more polar groups), when used in stoichiometric quantities act as complexing agents for transition metal cations.

Surprisingly however, it has been discovered that when used in low concentrations in the vanadium redox electrolyte solution, their ability to absorb on the surface of the charged nuclei causes them to act as inhibitors for precipitation, thus allowing stable supersaturated solutions to be prepared.

Other inorganic compounds which have the same properties include:

Sulphimide, (NH₂SO₂)₃, imidosulphomide, NH(NH₂SO₂)₂, as well as ammonia derivatives of phosphorous acids, eg; H₂[PO₃NH₂], H[OP—OH—NH], OP—NH—NH₂, OPN, O₃P₂OH(NH₂)₃, and HNP₂—O₂ NH (NH₂)₂ and thiophosphoric acid derivatives eg: PS(NH₂)₃.

Several methods for preparing stabilized vanadium electrolyte solutions are described in the present application. These methods can be used directly to prepare the supersaturated solutions of V³⁺/V(IV) ions. Alternatively, a 2M vanadium solution can be prepared by any of these methods in the presence of the stabilising agent. The supersaturated solution can then be prepared by removing the appropriate amount of water by evaporation, pervaporation or by boiling either at atmospheric pressure or under vacuum until the desired vanadium concentration is reached. Such a process would allow stable supersaturated solutions to be prepared for direct application in the vanadium redox cell.

Further concentrations of the vanadium electrolyte solution can also be undertaken, however either by addition or excess V₂O₅ power during electrolytic or chemical reduction, or by further evaporation or boiling, so as to produce a V³⁺/V(IV) vanadium electrolyte solution concentrate in the form of a slurry or gel. Such a slurry or colloidal concentrate would allow huge volume and weight reductions to be achieved, thus allowing transport costs to be dramatically reduced. Before use in the vanadium battery, the electrolyte solution concentrate can readily be reconstituted simply by adding water until the desired concentration is obtained.

Preparation of the electrolyte solution concentration takes place at elevated temperatures (above 40° C.) at which the V(II), V(III) and/or V(IV) vanadium ions are in solution. Cooling to room temperature will lead to the formation of a colloidal suspension or vanadium sulphate slurry in the supporting electrolyte solution. Typically, the vanadium content would be in the range 5–20 moles per litre of slurry. The electrolyte solution concentration could be readily reconstituted before use in the vanadium redox battery simply by adding water or dilute acid with or without slight heating to aid redissolution.

A 15M vanadium concentrate can be prepared by slowly adding V₂O₅ powder to 15M H₂SO₄ plus 0.1% fructose stabilising agent in the negative compartment of an electrolysis cell at 60° C. until all of the V₂O₅ has been dissolved and reduced to a 50:50 mixture of V³⁺ and V(IV) in H2SO4. On cooling to room temperature, the concentrate sets to form a colloidal paste but on reheating to 50° C. and adding water or dilute acid, a 5M stabilised solution can be prepared for the vanadium redox cell.

Example 13

A large number of compounds were screened as potential stabilising agents for V(V) solutions by adding 0.03 g of each to separate vials containing 25 ml of 2M V(V) solution in 4M H₂SO₄. These vials were placed in a water bath at 45° C. for up to 20 days after which time they were removed and left to stand at room temperature for a further 15–23 days. The solutions were then reduced to a lower oxidation state with zinc and titrated with potassium permanganate to determine the final vanadium concentration and the results are shown in the following table:

Studies of V⁵⁺ 25 ml 2 M at 45° C. & 0.03 g Additive Vial 20 days at 45° C. then room No. Additive temperature for t = ? days 101 control - no additive 0.83 M 103 starch 1.25 M dark green t = 15 days 105 glycerol 1.6 M dark green, t = 15 days 107 sorbitol 1.08 M dark green, t = 15 days 109 myo-inositol (INSOL) 1.17 M dark green, t = 15 days 111 methyl α-β-gluco-pyranoside 1.16 M dark green, t = 15 days 113 mannitol 1.18 M dark green, t = 15 days 115 lactose 1.629 M dark green, t = 16 days 117 D-fructose 1.12 M dark green, t = 16 days 119 D-glucose 0.889 M dark green, t = 16 days 121 methyl-α-D-glucopyranoside 0.699 M dark green, t = 16 days 123 D gluconic acid (Na) 1.037 M dark green, t = 16 days 125 succinic acid 0.847 M (green/yellow) t = 16 days 127 malic acid (Fizz) 0.984 M dark green, t = 16 days 129 L-ascorbic acid 1.13 M dark green, t = 16 days 131 citric acid 1.06 M dark green, t = 16 days 133 trisodium citrate 0.932 M dark green, yellow, t = 16 days 135 tartaric acid 0.9411 M dark green, t = 16 days 137 polytetrahydrofuran 0.996 M dark green, t = 16 days 139 furfural 1.22 M dark green, t = 16 days 141 sodium dodecyl sulphate (Fizz) 0.897 M green/yellow, t = 16 days 143 sodium lauryl sulphate 0.883 M dark green, t = 16 days 145 poly 4-styrene 0.99 M yellow/green, t = 19 days 147 urea 0.89 M yellow/green, t = 19 days 149 thiourea 1.19 M dark green, t = 19 days 151 ethanolamine 1.095 M dark green, t = 19 days 153 glycine 1.011 M dark green, t = 19 days 155 nitrilotriacetic acid 0.989 M dark green, t = 19 days 157 ethylenediaminetetraacetic acid 0.997 M green/yellow, t = 19 days 159 di(2-ethylhexyl) phosphate 0.68 M green/yellow, t = 19 days 161 boric oxide 0.918 M green/yellow, t = 19 days 163 H3PO4 0.995 M green/yellow, t = 19 days 165 ammonium oxalate 1.014 M green/yellow, t = 21 days 167 ammonium sulphate 1.00 M green/yellow, t = 21 days 169 potassium persulphate 1.03 M yellow/brown, t = 21 days 171 glycylglycin 0.95 M mid green, t = 21 days 173 α-N-benzoyl DL-alanine 0.97 M yellow/green, t = 21 days 175 phenylalanine 0.94 M yellow/green, t = 21 days 177 D-lysine 0.896 M yellow/green, t = 21 days 179 L-cystine 0.94 M dark green, t = 21 days 181 aspartic acid Not liquid - not titratable 183 glutamic acid 9 days at 45° C. followed by 23 days at room temperature 185 L-histidine mono HCl mono 14 1.18 M mid green 187 asparagine 1.403 M dark green 189 iso-isoleucine 1.210 M mid green-brown 191 glutamine 1.230 M dark green.

Example 14

Several additional compounds were screened by adding 1 wt. % to a 2M V(V) solution in M.H₂SO₄ and placing in a water bath at 44° C. to observe any colour change (indicating reduction of the V(V)) and the appearance of any precipitate. The following compounds were screened in this manner:

50A Briquest 301-50A (nitrilotris(methylene-phosphonic acid) 25K Briquest 3010-25K (potassium nitrilotris(methylenephosphonate)- N-oxide) 32S Briquest 301-325 (sodium nitrilotris(methylenephosphonate)). D1 sodium tripolyphosphate C1 sodium hexametaphosphate B1 sodium acid pyrophosphate

The results are summarised in the following table:

Additive wt % Appearance after x days at 44° C. 1 day 2 days 3 days 8 days 16 days Blank yellow, yellow, more yellow, more large solid slight precipitate precipitate amount of precipitate precipitate Arrowroot 1 dark blue, no dark blue, no blue/black, blue/black, blue/black, precipitate precipitate no no no precipitate precipitate precipitate Gelatin 1 blue/yellow, blue/black, no blue/black, blue/black, blue/black, no precipitate no no no precipitate precipitate precipitate precipitate 50A 1 blue/yellow, dark yellow, dark yellow, dark yellow, dark yellow, no no precipitate no very slight very slight precipitate precipitate precipitate precipitate 25K 1 yellow, dark yellow, dark yellow, dark yellow, yellow, slight no precipitate slight very slight more precipitate precipitate precipitate precipitate ³²S 1 yellow, no dark yellow, dark yellow, dark yellow, dark yellow precipitate no precipitate slight very slight slight precipitate precipitate precipitate H₃PO₄ 1 yellow, yellow, slight yellow, more yellow, yellow, slight precipitate precipitate more more precipitate precipitate precipitate D1 1 yellow, no yellow, no yellow, no yellow, yellow, precipitate precipitate precipitate slight slight precipitate precipitate C1 1 yellow, no yellow, no yellow, no yellow, very yellow, precipitate precipitate precipitate slight slight precipitate precipitate B1 1 yellow, no yellow, no yellow, no yellow, very yellow, precipitate precipitate precipitate slight slight precipitate precipitate

Example 15

A large number of compounds were screened as stabilising agents for V(II) solutions by adding 1 wt. % to a 2M V(II) solution in 3M H₂SO₄ and leaving at ambient temperature for eleven weeks, after which each sample was inspected for the presence of any precipitate. The results are given in the following table which shows that of the compounds tested, D-fructose, D-glucose, thiourea, tartaric acid, ammonium oxalate, ammonium sulphate, potassium persulphate, glycylglycin, 2 N-benzoyl DL-alanine, phenylalanine, D-lycine, L-cystine, asparatic acid, L-histidine, asparagine, D-L iso-isoleucine and glutamine are effective in inhibiting precipitation of V(II).

2 M V²⁺ 25 ml at Room Temperature + 0.003 g Vial No. Additive Appearance on Feb. 5, 1995 200 control Slight precipitate 202 starch Moderate precipitate 204 glycerol Moderate precipitate 206 sorbitol Slight precipitate 208 myo inositol Moderate precipitate 210 mannitol Significant precipitate 212 lactose Moderate precipitate 214 D-fructose Purple solution, no precipitate * 216 D-glucose Purple solution, no precipitate * 218 methyl α D-glucopyranoside Moderate precipitate 220 D-gluconic acid Moderate precipitate 222 succinic acid Slight precipitate 224 malic acid Slight precipitate 226 ascorbic acid Moderate precipitate 228 citric acid Moderate precipitate 230 trisodium citrate Moderate precipitate 232 tartaric acid Purple solution, no precipitate 234 polytetrahydrofuran Moderate precipitate 236 furfural Slight precipitate 238 sodium dodecyl sulphate Many bubbles, moderate precipitate 240 sodium lauryl sulphate Slight precipitate 242 poly 4-sytrene sulphonate Slight precipitate 244 urea Moderate precipitate 246 thiourea Black/purple solution, no precipitate * 248 ethanolamine Moderate precipitate 250 glycine Some bubbles, moderate precipitate 252 nitrilotriacetic acid Slight gas, slight precipitate 254 EDTA Slight precipitate 256 DL-(2-ethylhexyl) PO4 Gas, slight precipitate 258 boric acid Slight precipitate 260 phosphoric acid Slight precipitate 262 ammonium oxalate Purple solution, no precipitate * 264 ammonium sulphate Purple solution, no precipitate * 266 potassium persulphate Purple solution, no precipitate * 268 glycylglycine Purple solution, no precipitate * 270 2 N-benzoyl DL-alanine Purple solution, no precipitate * 272 phenylalanine Purple solution, no precipitate * 274 D-lycine HCl Purple solution, no precipitate * 276 L-cystine Purple solution, no precipitate * 278 aspartic acid Purple solution, no precipitate * 280 glutamic acid Purple solution, slight precipitate 282 L-histidine HCl H2O Purple solution, no precipitate * 284 asparagine Purple solution, no precipitate * 286 DL-iso-isoleucine Purple solution, no precipitate * 288 glutamine Purple solution, no precipitate * 

1. A vanadium high energy density (“HED”) electrolyte colloidal concentrate or slurry comprising vanadium redox ions in a concentration of greater than 3M and an electrolyte.
 2. The vanadium HED electrolyte colloidal concentrate or slurry according to claim 1, wherein the vanadium redox ions are present in the electrolyte colloidal concentate or slurry at a concentration of between 3.5 and 18.5M.
 3. The vanadium HED electrolyte colloidal concentrate or slurry according to claim 2, wherein the vanadium redox ions are present in the electrolyte colloidal concentrate or slurry at a concentration of between 3.5M and 8M.
 4. The vanadium HED electrolyte colloidal concentrate or slurry according to claim 2, wherein the vanadium redox ions are present in the electrolyte colloidal concentrate or slurry at a concentration of between 3.5M and 5M.
 5. The vanadium HED electrolyte colloidal concentrate or slurry according to claim 1, wherein the vanadium redox ions are present in the electrolyte colloidal concentrate or slurry at a concentration of between 5M and 18.5M.
 6. The vanadium HED electrolyte colloidal concentrate or slurry according to claim 5, wherein the vanadium redox ions are present in the electrolyte colloidal concentrate or slurry at a concentration of between 5M and 8M.
 7. The vanadium HED electrolyte colloidal concentrate or slurry according to claim 1 wherein the colloidal concentrate or slurry comprises an aqueous colloidal concentrate or slurry.
 8. The vanadium HED electrolyte colloidal concentrate or slurry according to claim 7 wherein the electrolyte is selected from the group consisting of H₂SO₄, trifluoromethanesulphonic acid, Na₂SO₄, ammonium sulphate, K₂SO₄, H₃PO₄, Na₃PO₄, K₃PO₄, KNO₃, NaNO₃, sulphonic acid, a C₆–C₁₄ arylsulphonic acid, a C₁–C₆ alkylsulphonic acid, acetic acid and mixtures thereof.
 9. The vanadium HED electrolyte colloidal concentrate or slurry according to claim 1 wherein the electrolyte comprises at least about 5M H₂SO₄ or total sulphate.
 10. The vanadium HED electrolyte colloidal concentrate or slurry according to claim 1 wherein the electrolyte comprises 4–9M H₂SO₄ or total sulphate.
 11. The vanadium HED electrolyte colloidal concentrate or slurry according to claim 10 wherein the electrolyte comprises 5–7M H₂SO₄ or total sulphate.
 12. The vanadium HED electrolyte colloidal concentrate or slurry according to claim 1, wherein the vanadium redox ions are selected from the group consisting of pentavalent vanadium ions, tetravalent vanadium ions, trivalent vanadium ions, divalent vanadium ions, a mixture of divalent and trivalent vanadium ions, a mixture of divalent and tetravalent vanadium ions, a mixture of trivalent and tetravalent vanadium ions, a mixture of divalent, trivalent and tetravalent vanadium ions, a mixture of divalent, trivalent, tetravalent and pentavalent vanadium ions, a mixture of trivalent, tetravalent and pentavalent vanadium ions and a mixture of tetravalent and pentavalent vanadium ions.
 13. The vanadium RED electrolyte colloidal concentrate or slurry according to claim 12 comprising a 50:50 ratio of trivalent and tetravalent vanadium ions.
 14. The vanadium RED electrolyte colloidal concentrate or slurry according to claim 1 wherein the electrolyte colloidal concentrate or slurry further comprises a stabilizing amount of a stabilizing agent.
 15. The vanadium RED electrolyte colloidal concentrate or slurry according to claim 14 wherein the stabilizing agent is selected from the group consisting of inorganic phosphates and ammonium compounds.
 16. The vanadium RED electrolyte colloidal concentrate or slurry according to claim 15 wherein the ammonium compound is ammonium sulphate.
 17. The vanadium RED electrolyte colloidal concentrate or slurry of claim 1, further comprising an effective immobilizing amount of an immobilizing agent.
 18. The vanadium RED electrolyte colloidal concentrate or slurry of claim 17, wherein the immobilizing agent is selected from the group consisting of gels, gums, Xanthan gum, Guar gum, starch, furcellaran, hypnean, dextran, tamarind, alginates, pectic gels, sodium pectate, alkylcellulose, hydrophilic colloids, hydroxyalkylcellulose, carboxyalkylcellulose, hydroxypropylmethylcellulose, sodium carboxymethylcellulose, potassium carboxymethylcellulose, hydroxymethylcellulose, ethyl succinylated cellulose, succinylated zein, carboxymethylcellulose, sodium poly(styrene sulphonate) with poly(vinyl methyl pyridinium) chloride, sodium poly(styrene sulphonate) with poly(vinyl benzyl trimethyl ammonium) chloride, vinyl acetate homopolymer, polyvinyl alcohol resin, carboxypolymethylene, sodium alginate, a mixture of gelatin and sodium alginate, potassium alginate, gelatine, acacia gum, deacetylated gellan gum, karaya gum, locust bean gum, tragacanth gum, agar, algin, carrageenin, carob bean gum, oat gum, pectin, methyl cellulose, hydroxypropylmethyl cellulose, polygalacturonic acid and mixtures thereof. 